Startup and update sequence

1. Version mismatch restart loop (pkg/hooks/worker.go):
    - Added versionsCompatible() and extractBaseVersion() functions
    - Hooks no longer restart worker when base versions match (e.g., v0.3.5-dirty ≈ v0.3.5-2-gca711a8-dirty)
2. Auto-update detection (internal/update/update.go):
    - isNewerVersion() now extracts base version before comparing
    - No longer always reports updates for dirty/dev builds
3. Non-blocking ChromaDB sync (internal/worker/handlers.go):
    - SyncUserPrompt now runs in a goroutine with 10-second timeout
    - /api/sessions/init responds immediately without waiting for ChromaDB

Makefile

@@ -27,6 +27,7 @@ dashboard:
 	@cd ui && npm install --silent && npm run build
 	@rm -rf internal/worker/static
 	@mkdir -p internal/worker/static
+	@touch internal/worker/static/placeholder.html
 	@cp -r ui/dist/* internal/worker/static/
 
 # Build worker service