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/src/monaco-setup.ts

@@ -0,0 +1,76 @@
+import { loader, type Monaco } from "@monaco-editor/react";
+import * as monaco from "monaco-editor";
+import editorWorker from "monaco-editor/esm/vs/editor/editor.worker?worker";
+
+let initialized = false;
+let monacoPromise: Promise<Monaco> | null = null;
+
+// A Monarch tokenizer for Typst covering the common surface (headings,
+// script keywords, math, comments, emphasis, strings, raw blocks). This is
+// syntax-only; the LSP additionally provides diagnostics and (optionally)
+// semantic tokens.
+const typstLanguageDefinition: monaco.languages.IMonarchLanguage = {
+  defaultToken: "",
+  tokenPostfix: ".typst",
+  brackets: [
+    { open: "(", close: ")", token: "delimiter.parenthesis" },
+    { open: "[", close: "]", token: "delimiter.square" },
+    { open: "{", close: "}", token: "delimiter.curly" },
+  ],
+  tokenizer: {
+    root: [
+      [/^=+\s.*$/, "keyword.heading"],
+      [/\*[^*]+\*/, "string.emphasis"],
+      [/_[^_]+_/, "string.emphasis"],
+      [/\/\/.*$/, "comment"],
+      [/\/\*/, "comment", "@comment"],
+      [/#\w+/, "keyword"], // #set, #let, #show, #if, ...
+      [/\$/, { token: "string", next: "@math" }],
+      [/"/, "string", "@string"],
+      [/[{}()\[\]]/, "@brackets"],
+    ],
+    comment: [
+      [/\*\//, "comment", "@pop"],
+      [/[^*]+/, "comment"],
+      [/\*/, "comment"],
+    ],
+    math: [
+      [/\$/, { token: "string", next: "@pop" }],
+      [/\\[a-zA-Z]+/, "keyword"],
+      [/[a-zA-Z]+/, "variable"],
+      [/[^\$]/, "string"],
+    ],
+    string: [
+      [/[^"]/, "string"],
+      [/"/, "string", "@pop"],
+    ],
+  },
+};
+
+function initEnvironment(): void {
+  if (initialized) return;
+  // Vite bundles the editor worker via `?worker`. Monaco only needs the base
+  // editor worker for plaintext/typst (no language-specific workers required).
+  self.MonacoEnvironment = {
+    getWorker: () => new editorWorker(),
+  };
+  loader.config({ monaco });
+  initialized = true;
+}
+
+export function loadMonaco(): Promise<Monaco> {
+  if (!monacoPromise) {
+    initEnvironment();
+    // loader.init() resolves to the same `monaco` instance we configured above.
+    monacoPromise = loader.init().then((m) => {
+      m.languages.register({ id: "typst" });
+      m.languages.setMonarchTokensProvider("typst", typstLanguageDefinition);
+      return m;
+    });
+  }
+  return monacoPromise;
+}
+
+export function getMonaco(): Monaco {
+  return monaco as unknown as Monaco;
+}