feat(FN-1401): integrate PluginRunner into runtime lifecycle
- Integrate PluginRunner into InProcessRuntime for plugin lifecycle management
- Wire plugin:created, plugin:updated, plugin:deleted events through runtime event bus
- Add plugin tools to StepSessionExecutor so plugins can provide tools during step execution
- Fix PluginRunner to pass PluginContext to task lifecycle hooks (onTaskCreated, onTaskUpdated, etc.)
- Add PluginRunner tests covering init/shutdown, timeout isolation, and sync event behavior
- Add InProcessRuntime tests verifying plugin integration
- Update memory documentation with plugin runner lifecycle wiring
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