fix(a11y): add accessibility and UX polish to DirectoryPicker

- Add role="dialog", aria-modal, aria-label to the modal panel
- Add aria-label to close button, home button
- Add aria-hidden to decorative icons (chevrons, backdrop)
- Add role="status" to loading spinner with sr-only label
- Add role="alert" to error state
- Add aria-current="location" to active breadcrumb segment
- Wrap breadcrumb in nav landmark with aria-label
- Add Escape key handler to dismiss the modal
- Auto-focus the modal panel on open
- Add focus-visible ring styles to all interactive elements
  (matches existing focus-visible:ring-2 ring-accent/40 pattern)
- Increase breadcrumb button padding (px-1.5 py-1) for better
  touch targets
- Increase directory entry padding (py-2.5) for touch comfort
- Add active:bg-hover/70 pressed state on directory entries
- Add active:bg-accent/80 pressed state on select button

gitnexus-web/src/components/DirectoryPicker.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, useCallback } from 'react';
+import { useState, useEffect, useCallback, useRef } from 'react';
 import { Folder, ChevronRight, Home, X, Loader2, AlertCircle, Check } from '@/lib/lucide-icons';
 import { listDirectories, type DirEntry } from '../services/backend-client';
 import { useTranslation } from 'react-i18next';
@@ -17,6 +17,7 @@ export const DirectoryPicker = ({ open, onClose, onSelect, initialDir }: Directo
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const [isVisible, setIsVisible] = useState(false);
+  const panelRef = useRef<HTMLDivElement>(null);
 
   const fetchEntries = useCallback(async (dir: string) => {
     setLoading(true);
@@ -41,6 +42,24 @@ export const DirectoryPicker = ({ open, onClose, onSelect, initialDir }: Directo
     }
   }, [open, initialDir, fetchEntries]);
 
+  useEffect(() => {
+    if (!open) return;
+    const handleKeyDown = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') {
+        e.stopPropagation();
+        onClose();
+      }
+    };
+    document.addEventListener('keydown', handleKeyDown);
+    return () => document.removeEventListener('keydown', handleKeyDown);
+  }, [open, onClose]);
+
+  useEffect(() => {
+    if (open && panelRef.current) {
+      panelRef.current.focus();
+    }
+  }, [open]);
+
   if (!open) return null;
 
   const segments = currentDir.split('/').filter(Boolean);
@@ -59,11 +78,17 @@ export const DirectoryPicker = ({ open, onClose, onSelect, initialDir }: Directo
       <div
         className={`absolute inset-0 bg-black/60 backdrop-blur-sm transition-opacity duration-200 ${isVisible ? 'opacity-100' : 'opacity-0'}`}
         onClick={onClose}
+        aria-hidden="true"
       />
 
       <div
+        ref={panelRef}
         data-testid="directory-picker-modal"
-        className={`relative mx-4 flex w-full max-w-lg flex-col overflow-hidden rounded-2xl border border-border-subtle bg-surface shadow-2xl transition-all duration-200 ${isVisible ? 'scale-100 opacity-100' : 'scale-95 opacity-0'}`}
+        role="dialog"
+        aria-modal="true"
+        aria-label={t('repoAnalyzer.directoryPicker.title')}
+        tabIndex={-1}
+        className={`relative mx-4 flex w-full max-w-lg flex-col overflow-hidden rounded-2xl border border-border-subtle bg-surface shadow-2xl transition-all duration-200 outline-none ${isVisible ? 'scale-100 opacity-100' : 'scale-95 opacity-0'}`}
         style={{ maxHeight: '70vh' }}
       >
         {/* Header */}
@@ -73,27 +98,33 @@ export const DirectoryPicker = ({ open, onClose, onSelect, initialDir }: Directo
           </h3>
           <button
             onClick={onClose}
-            className="p-1 text-text-muted transition-colors hover:text-text-primary"
+            aria-label="Close"
+            className="rounded-md p-1.5 text-text-muted transition-colors hover:text-text-primary focus-visible:ring-2 focus-visible:ring-accent/40 focus-visible:outline-none"
           >
             <X className="h-4 w-4" />
           </button>
         </div>
 
         {/* Breadcrumb */}
-        <div className="flex items-center gap-1 overflow-x-auto border-b border-border-subtle bg-elevated/50 px-5 py-2.5">
+        <nav
+          aria-label="Directory breadcrumb"
+          className="flex items-center gap-1 overflow-x-auto border-b border-border-subtle bg-elevated/50 px-5 py-2"
+        >
           <button
             data-testid="directory-picker-home"
             onClick={() => navigateTo('/')}
-            className="shrink-0 rounded p-0.5 text-text-muted transition-colors hover:text-accent"
+            aria-label="Root directory"
+            className="shrink-0 rounded-md p-1.5 text-text-muted transition-colors hover:text-accent focus-visible:ring-2 focus-visible:ring-accent/40 focus-visible:outline-none"
           >
             <Home className="h-3.5 w-3.5" />
           </button>
           {segments.map((seg, i) => (
             <span key={i} className="flex shrink-0 items-center gap-1">
-              <ChevronRight className="h-3 w-3 text-text-muted/50" />
+              <ChevronRight className="h-3 w-3 text-text-muted/50" aria-hidden="true" />
               <button
                 onClick={() => handleBreadcrumbClick(i)}
-                className={`rounded px-1 py-0.5 font-mono text-xs transition-colors ${
+                aria-current={i === segments.length - 1 ? 'location' : undefined}
+                className={`rounded-md px-1.5 py-1 font-mono text-xs transition-colors focus-visible:ring-2 focus-visible:ring-accent/40 focus-visible:outline-none ${
                   i === segments.length - 1
                     ? 'font-medium text-text-primary'
                     : 'text-text-muted hover:text-accent'
@@ -103,25 +134,26 @@ export const DirectoryPicker = ({ open, onClose, onSelect, initialDir }: Directo
               </button>
             </span>
           ))}
-        </div>
+        </nav>
 
         {/* Directory listing */}
         <div data-testid="directory-listing" className="min-h-[200px] flex-1 overflow-y-auto px-2 py-2">
           {loading && (
-            <div className="flex items-center justify-center py-12">
+            <div className="flex items-center justify-center py-12" role="status">
               <Loader2 className="h-5 w-5 animate-spin text-text-muted" />
+              <span className="sr-only">Loading directories...</span>
             </div>
           )}
 
           {error && !loading && (
-            <div className="flex flex-col items-center gap-2 py-12 text-center">
+            <div className="flex flex-col items-center gap-2 py-12 text-center" role="alert">
               <AlertCircle className="h-5 w-5 text-red-400" />
               <p className="text-xs text-red-400">{error}</p>
               <button
                 onClick={() =>
                   navigateTo(currentDir === '/' ? '/' : currentDir.replace(/\/[^/]+$/, '') || '/')
                 }
-                className="mt-1 text-xs text-text-muted underline hover:text-text-secondary"
+                className="mt-1 rounded-md px-2 py-1 text-xs text-text-muted underline transition-colors hover:text-text-secondary focus-visible:ring-2 focus-visible:ring-accent/40 focus-visible:outline-none"
               >
                 {t('repoAnalyzer.directoryPicker.goBack')}
               </button>
@@ -144,13 +176,13 @@ export const DirectoryPicker = ({ open, onClose, onSelect, initialDir }: Directo
                   key={entry.name}
                   data-testid={`dir-entry-${entry.name}`}
                   onClick={() => navigateTo(target)}
-                  className="flex w-full items-center gap-2.5 rounded-lg px-3 py-2 text-left transition-colors hover:bg-hover"
+                  className="flex w-full items-center gap-2.5 rounded-lg px-3 py-2.5 text-left transition-colors hover:bg-hover active:bg-hover/70 focus-visible:ring-2 focus-visible:ring-accent/40 focus-visible:outline-none"
                 >
                   <Folder className="h-4 w-4 shrink-0 text-accent/70" />
                   <span className="truncate font-mono text-xs text-text-secondary">
                     {entry.name}
                   </span>
-                  <ChevronRight className="ml-auto h-3 w-3 shrink-0 text-text-muted/40" />
+                  <ChevronRight className="ml-auto h-3 w-3 shrink-0 text-text-muted/40" aria-hidden="true" />
                 </button>
               );
             })}
@@ -164,7 +196,7 @@ export const DirectoryPicker = ({ open, onClose, onSelect, initialDir }: Directo
           <button
             data-testid="directory-picker-select"
             onClick={() => onSelect(currentDir)}
-            className="flex shrink-0 items-center gap-1.5 rounded-lg bg-accent px-3.5 py-2 text-xs font-medium text-white transition-colors hover:bg-accent/90"
+            className="flex shrink-0 items-center gap-1.5 rounded-lg bg-accent px-3.5 py-2 text-xs font-medium text-white transition-colors hover:bg-accent/90 active:bg-accent/80 focus-visible:ring-2 focus-visible:ring-accent/40 focus-visible:ring-offset-2 focus-visible:ring-offset-surface focus-visible:outline-none"
           >
             <Check className="h-3.5 w-3.5" />
             {t('repoAnalyzer.directoryPicker.select')}