feat: editor improvements and architectural grid prototype

Multiple feature additions and improvements across the application:

- NextGen Editor: drag handles, smart paste, block actions
- Structured views: Kanban and table layouts for notes
- Architectural Grid: new brainstorming/agent interface prototype
- Flashcards: SM-2 revision algorithm with AI generation
- MCP server: robustness improvements
- Graph/PDF chat: fix click propagation and copy behavior
- Various UI/UX enhancements and bug fixes

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

architectural-grid1/metadata.json

@@ -0,0 +1,6 @@
+{
+  "name": "Architectural Grid",
+  "description": "A minimalist notebook for architectural research and conceptual sketches, featuring a Wave Brainstorming radial canvas for AI-powered idea exploration.",
+  "requestFramePermissions": [],
+  "majorCapabilities": []
+}