Merge pull request #29 from typelets/feature/mermaid-diagrams

Adds Mermaid.js diagram support with Monaco editor, live preview, and export tools. Includes 6 templates, zoom/pan controls, theme-aware rendering, and clipboard/file export. New "Diagrams" filter in notes panel with visual indicators. 

Backward compatible - adds optional `type?: 'note' | 'diagram'` to Note interface.

Mobile: Simplified architecture by removing offline-first complexity (15+ files), refactored screen structure for better maintainability.

Author: typelets

package.json

@@ -94,6 +94,7 @@
     "highlight.js": "^11.11.1",
     "lowlight": "^3.3.0",
     "lucide-react": "^0.544.0",
+    "mermaid": "^11.12.1",
     "monaco-editor": "^0.53.0",
     "react": "^19.1.1",
     "react-dom": "^19.1.1",