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/worker/OpenRouterAgent.ts

@@ -345,7 +345,7 @@ export class OpenRouterAgent {
       return;
     }
 
-    logger.failure('SDK', 'OpenRouter agent error', { sessionDbId: session.sessionDbId }, error as Error);
+    logger.failure('SDK', 'OpenRouter agent error', { sessionDbId: session.sessionDbId }, error instanceof Error ? error : new Error(String(error)));
     throw error;
   }