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/sqlite/migrations/runner.ts

@@ -421,7 +421,7 @@ export class MigrationRunner {
     try {
       this.createUserPromptsFTS();
     } catch (ftsError) {
-      logger.warn('DB', 'FTS5 not available — user_prompts_fts skipped (search uses ChromaDB)', {}, ftsError instanceof Error ? ftsError : undefined);
+      logger.warn('DB', 'FTS5 not available — user_prompts_fts skipped (search uses ChromaDB)', {}, ftsError instanceof Error ? ftsError : new Error(String(ftsError)));
     }
 
     // Commit transaction