Initial scaffold: pnpm workspace monorepo with backend + frontend

- Backend: Express + WebSocket proxy (tsx watch, strict TS, ESM)
- Frontend: React 19 + Vite + Monaco + Tailwind v4 + Tauri v2
- pnpm workspace at root for single-install workflow
- AGENTS.md with architectural constraints and commands
- Removed Tauri greet demo, added minimal App shell
- No external database, Git-as-Database philosophy

typst-leaf-frontend/src-tauri/capabilities/default.json

@@ -0,0 +1,10 @@
+{
+  "$schema": "../gen/schemas/desktop-schema.json",
+  "identifier": "default",
+  "description": "Capability for the main window",
+  "windows": ["main"],
+  "permissions": [
+    "core:default",
+    "opener:default"
+  ]
+}