feat: Release v4.0.0 - Plugin data directory and auto-starting worker

BREAKING CHANGES:
- Data directory moved from ~/.claude-mem/ to ${CLAUDE_PLUGIN_ROOT}/data/
- Fresh start required - no migration from v3.x databases
- Worker service now auto-starts on SessionStart hook

New Features:
- MCP Search Server with 6 specialized search tools
- FTS5 full-text search across observations and sessions
- Auto-starting worker service in SessionStart hook
- Citation support for search results (claude-mem:// URIs)

Changes:
- Updated paths.ts to use CLAUDE_PLUGIN_ROOT for data directory
- Added worker auto-start logic to context hook
- Updated worker service to write port file to plugin data dir
- Bumped version to 4.0.0 in package.json and plugin.json
- Created comprehensive CHANGELOG.md documenting v4.0.0 changes
- Updated README.md with v4.0.0 breaking changes and features
- Rebuilt all hooks and worker service

Technical Improvements:
- Improved error handling and graceful degradation
- Structured logging across all components
- Enhanced plugin integration with Claude Code

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

plugin/.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "claude-mem",
-  "version": "3.9.17",
+  "version": "4.0.0",
   "description": "Persistent memory system for Claude Code - seamlessly preserve context across sessions",
   "author": {
     "name": "Alex Newman"