* feat: Implement MCP manager for server connections, tool registration, and deferred tool loading for agents.
* feat: Add tests for deferred tool activation logic within the tool registry and agent loop.
* fix(mcp): prevent deny list bypass via lazy activation + fix idempotency race
- Add PolicyEngine.IsDenied() to check deny patterns (incl. group: expansion)
before allowing lazily-activated deferred tools to execute
- Check IsDenied() in both single-tool and parallel execution paths in loop.go
- Make ActivateToolIfDeferred idempotent by checking activatedTools before
returning false, preventing concurrent goroutines from being blocked
- Add tests for deny-on-first-call, group deny patterns, and idempotent
concurrent activation
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Co-authored-by: viettranx <viettranx@gmail.com>
