feat(FN-1532): add performance indexes for dashboard boot queries

- Add composite indexes for dashboard boot query paths
- Optimize taskList queries with (column, updatedAt) and (column, status, updatedAt) indexes
- Optimize activityLog queries with (timestamp DESC, taskId) index
- Add idempotent CREATE INDEX IF NOT EXISTS pattern for migrations
- Document index patterns in memory.md for future schema changes
- Update schema version assertions in db.test.ts and task-documents.test.ts
- Add changeset for dashboard load performance improvement

packages/core/src/run-audit.test.ts

@@ -464,8 +464,8 @@ describe("Run Audit", () => {
       expect(indexNames).toContain("idxRunAuditEventsTimestamp");
     });
 
-    it("schema version is bumped to 25", () => {
-      expect(db.getSchemaVersion()).toBe(27);
+    it("schema version is bumped to 28", () => {
+      expect(db.getSchemaVersion()).toBe(28);
     });
   });
 });