feat: add local datetime support and automated updated_at trigger for items table

docs: update README and add development journal for Gemma 3 integration

chore: migrate to Tauri/Rust backend with SeaORM and add unit/integration tests ...

- Migrated Electron/Bun backend to Rust (Tauri v2).
- Integrated SeaORM with SQLite and sqlite-vec support.
- Implemented unit tests for LlamaClient and database initialization.
- Added integration tests for MCP handlers.
- Updated documentation (README.md, walkthrough, implementation plan).
- Improved dev environment with launch scripts and tasks.
- Followed user global rules for journaling and gitignore.

refactor: modernize source code with improved structure and logging ...

- Add config.js for centralized configuration management
- Add logger.js for structured logging with levels
- Modernize main.js with JSDoc comments and error handling
- Enhance mcp-server.js with health check endpoint and logging
- Refactor db.js with validation and error handling functions
- Add TOOL_NAMES constant and improve mcp-tools.js documentation
- Refactor mcp-handlers.js with modular handler functions
- Enhance llama-client.js with timeout and input validation
- Update test to match new error messages
- All 35 tests passing with improved code quality

Add MCP server with llama.cpp integration and docs