Fix logs --follow timeout by lowering SlateDB reader manifest poll interval

The default DbReaderOptions::manifest_poll_interval is 10s, which meant
the DbReader couldn't see conclusion/status updates from a detached run
until 10s after they were written. The nextest timeout (6s) fired first,
causing logs_follow_detached_run_streams_until_completion to always fail.
100ms is appropriate for local disk and in-memory object stores.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/crates/fabro-store/src/slate/mod.rs

@@ -71,7 +71,10 @@ impl SlateStore {
             db_prefix.to_string(),
             self.object_store.clone(),
             None,
-            DbReaderOptions::default(),
+            DbReaderOptions {
+                manifest_poll_interval: Duration::from_millis(100),
+                ..DbReaderOptions::default()
+            },
         )
         .await?)
     }