#477 Memory Leak: Tool registry never cleaned

engine/tools/registry.py:103-104 ToolRegistry._tools dict grows unbounded: - App tools added dynamically (apps.{app_name}.{action_name}) - Old app versions not removed when replaced - Singleton lifespan = worker lifespan Over months with many app deployments, registry accumulates thousands of entries. FIX: Add tool aging/TTL or cleanup for deprecated app versions.