fix: resolve Greptile review comments on error handling

- Remove spurious console.error in logger JSON.parse catch (expected control flow)
- Remove debug logging from hot PID cleanup loop (approved override)
- Replace unsafe `error as Error` casts with instanceof checks in ChromaSync, GeminiAgent, OpenRouterAgent
- Wrap non-Error FTS failures with new Error(String()) instead of dropping details

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

src/services/sync/ChromaSync.ts

@@ -565,7 +565,7 @@ export class ChromaSync {
     try {
       await this.runBackfillPipeline(db, backfillProject, existing);
     } catch (error) {
-      logger.error('CHROMA_SYNC', 'Backfill failed', { project: backfillProject }, error as Error);
+      logger.error('CHROMA_SYNC', 'Backfill failed', { project: backfillProject }, error instanceof Error ? error : new Error(String(error)));
       throw new Error(`Backfill failed: ${error instanceof Error ? error.message : String(error)}`);
     } finally {
       db.close();