fix(web): clear document selection when the active space changes

The bulk-selection set (`selectedDocumentIds`) lived in AppExperience and was
only cleared on explicit "clear", on successful bulk delete, or never. Switching
spaces left the previous space's selected ids in the set while the grid rendered
a different space, so the selection toolbar still showed them and "Delete
selected" would permanently delete documents from another space that the user
could no longer see.

Clear the selection (and exit selection mode) whenever the active space changes.
The functional updates return the previous reference when there is nothing to
clear, so the initial mount doesn't cause needless re-renders.

apps/web/components/app-experience.tsx

@@ -294,6 +294,17 @@ export function AppExperience() {
 	)
 	const [isSelectionMode, setIsSelectionMode] = useState(false)
 
+	// Selection is scoped to the documents currently on screen. When the active
+	// space changes the previous selection points at documents from another
+	// space that are no longer visible, so clear it — otherwise "Delete selected"
+	// would delete documents the user can't see anymore.
+	const activeSpaceKey = selectedProjects.join("|")
+	// biome-ignore lint/correctness/useExhaustiveDependencies: reset only when the space changes, not on selection edits
+	useEffect(() => {
+		setSelectedDocumentIds((prev) => (prev.size === 0 ? prev : new Set()))
+		setIsSelectionMode((prev) => (prev ? false : prev))
+	}, [activeSpaceKey])
+
 	const handleToggleSelection = useCallback((documentId: string) => {
 		setSelectedDocumentIds((prev) => {
 			const next = new Set(prev)