feat: barebones MVP — editor, live LSP, and preview

Backend (typst-leaf-backend)
- REST API for multi-project file management under PROJECTS_ROOT
  (list/create projects, get file tree, read/write files; zod-validated
  sandbox prevents path traversal).
- LSP thin proxy: spawns a single tinymist lsp process, pipes one active
  WebSocket straight to its stdio via vscode-ws-jsonrpc. New connections
  trigger a takeover (old session disposed, fresh tinymist spawned).
- Live preview pipeline: the frontend sends tinymist.startDefaultPreview
  over the LSP wire, reads the returned data-plane port, and relays it to
  the backend. The backend proxies /preview (WS, with retry and an Origin
  header for typst-preview) and /preview-app (HTTP, injecting a script that
  rewrites the webview's WS path to /preview and forces light mode).
- Graceful SIGTERM/SIGINT shutdown.
- Auto-seeds a hello project on first boot.
- Removed execa dependency (no longer needed).

Frontend (typst-leaf-frontend)
- Monaco editor with typst syntax highlighting (Monarch tokenizer) and
  live LSP diagnostics (markers), completion, hover, definitions, and
  formatting — all driven by a raw JSON-RPC WebSocket client (no
  monaco-languageclient or vscode-api dependency).
- Project picker and file tree sidebar.
- Live preview pane: iframes the typst-preview webview through the
  backend's /preview-app proxy, so the pipedepeline works remotely.
- Monaco bundled locally (no CDN) with a Vite worker setup.
- Vite dev proxy so relative /api, /lsp, /preview, and /preVIEW-app URLs
  reach the backend on port 4000.
- Light-mode UI (editor 'vs' theme, white chrome).
- Prevent esbuild from tree-shaking monaco.editor services
  (optimizeDeps.esbuildOptions.treeShaking: false).

Infrastructure
- Added vscode-ws-jsonrpc to backend dependencies.
- Removed monaco-languageclient and vscode-ws-jsonrpc from frontend
  dependencies (replaced by the raw JSON-RPC client).
- Added monaco-editor as a direct frontend dependency.
- Updated README (correct frontend port 1420, tinymist install command,
  environment variables, architecture).
- Added projects/ to .gitignore.
- Renamed Tauri productName and page title to typst-leaf.

typst-leaf-frontend/vite.config.ts

@@ -8,6 +8,15 @@ const host = process.env.TAURI_DEV_HOST;
 // https://vite.dev/config/
 export default defineConfig(async () => ({
   plugins: [tailwindcss(), react()],
+  // Force esbuild to tree-shake as little as possible from monaco-editor.
+  // By default, Vite's pre-bundling applies tree-shaking which discards
+  // `monaco.languages.createDiagnosticCollection` and other standalone-editor
+  // services that we need at runtime.
+  optimizeDeps: {
+    esbuildOptions: {
+      treeShaking: false,
+    },
+  },
 
   // Vite options tailored for Tauri development and only applied in `tauri dev` or `tauri build`
   //
@@ -29,5 +38,19 @@ export default defineConfig(async () => ({
       // 3. tell Vite to ignore watching `src-tauri`
       ignored: ["**/src-tauri/**"],
     },
+    // Dev proxy: the SPA talks to the backend via relative URLs so that the
+    // same code works in dev (Vite :1420 → backend :4000) and in self-hosted
+    // prod (behind a reverse proxy). The preview webview and its WS are also
+    // proxied so the iframe is same-origin with the app.
+    proxy: {
+      "/api": "http://localhost:4000",
+      "/preview-app": {
+        target: "http://localhost:4000",
+        // the webview is HTML; rewrite so the path is preserved for upstream
+        ws: false,
+      },
+      "/lsp": { target: "ws://localhost:4000", ws: true },
+      "/preview": { target: "ws://localhost:4000", ws: true },
+    },
   },
 }));