fix: rebuild FTS5 index after bulk observation import (fixes #1631) (#1632)

Imported observations were invisible to the MCP search tool because the
FTS5 content table was not reliably updated during bulk import. The import
handler now calls rebuildObservationsFTSIndex() after inserting new
observations, ensuring the full-text search index is consistent.

A new SessionStore.rebuildObservationsFTSIndex() method encapsulates the
FTS5 rebuild command and is a no-op when the observations_fts table does
not exist (e.g. FTS5 unavailable on Windows).

src/services/sqlite/SessionStore.ts

@@ -2615,6 +2615,23 @@ export class SessionStore {
     return { imported: true, id: result.lastInsertRowid as number };
   }
 
+  /**
+   * Rebuild the FTS5 index for observations.
+   * Should be called after bulk imports to ensure imported rows are searchable.
+   * No-op if observations_fts table does not exist.
+   */
+  rebuildObservationsFTSIndex(): void {
+    const hasFTS = (this.db.prepare(
+      "SELECT name FROM sqlite_master WHERE type='table' AND name='observations_fts'"
+    ).all() as { name: string }[]).length > 0;
+
+    if (!hasFTS) {
+      return;
+    }
+
+    this.db.run("INSERT INTO observations_fts(observations_fts) VALUES('rebuild')");
+  }
+
   /**
    * Import user prompt with duplicate checking
    * Duplicates are identified by content_session_id + prompt_number