EvalPath-based loading of Go source directories with typed factory
functions for interface bridging (required by yaegi's wrapping model).
Supports all plugin capabilities: routes, events, and migrations.
Registers itself into the Manager via init() to avoid import cycles.
Add the core plugin system with four interfaces:
- Plugin: base lifecycle (Name, Version, Init, Shutdown)
- MigrationPlugin: database migrations
- AuthenticatedRouterPlugin: routes behind auth
- UnauthenticatedRouterPlugin: public routes
The Manager handles loading, initialization, shutdown, and route
registration. Includes native .so loader (marked deprecated) and
yaegi loader integration point.
