feat(core): add actions/events hook infrastructure to plugin-loader

[svallory]

Summary

• Adds actions (Record) and events (Record) hook types to the plugin-loader alongside existing array-based hooks
• Plugins can now export actions and events objects for WebSocket RPC and fire-and-forget messaging
• Defines PluginModule, ActionContext, ActionHandler, EventHandler, SourceTools, and related types in packages/core/src/types.ts
• Exports all types from @docmd/core

Context

Part of the plugin API infrastructure discussed in #73. This enables plugins to register server-side action handlers that respond to browser RPC calls during development. The action dispatcher (separate PR) will consume these hooks.

Changes

File	Change
packages/core/src/utils/plugin-loader.ts	Add actions: {} and events: {} to hooks, update reset loop, add merge logic in registerPlugin()
packages/core/src/types.ts	New file with all plugin API type definitions
packages/core/src/index.ts	Re-export types

Test plan

• Register a mock plugin with actions: { 'test:foo': handler } — verify hooks.actions['test:foo'] is callable
• Verify existing plugins continue to load (no regression on array hooks)
• Run pnpm test

[mgks]

Closing.
These changes are included in #97 which has been merged. Thank you for the clean PR chain! 🙏