feat: add pnpm store mount, pre-flight checks, and idle timeout for reviewer containers

- Detect pnpm projects and mount global store read-only so hardlinks resolve
- npm/yarn/bun need no extra mounts (node_modules is self-contained)
- Pre-flight check: verify Docker running + image exists (cached after first call)
- Add activity-based idle timeout (reset on stdout/stderr like host runner)
- Clean up orphaned containers on shutdown (not just startup)

src/index.ts

@@ -377,6 +377,7 @@ async function main(): Promise<void> {
       );
     }
     await queue.shutdown(10000);
+    cleanupOrphans();
     for (const ch of channels) await ch.disconnect();
     process.exit(0);
   };