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-backend/src/routes/projects.ts

@@ -0,0 +1,107 @@
+import { Router, type Router as ExpressRouter } from "express";
+import fs from "node:fs/promises";
+import path from "node:path";
+import { pathToFileURL } from "node:url";
+import { PROJECTS_ROOT } from "../config.js";
+import { projectDir, projectNameSchema } from "../paths.js";
+
+export const projectsRouter: ExpressRouter = Router();
+
+const MAX_TREE_DEPTH = 6;
+const MAX_TREE_ENTRIES = 2000;
+
+projectsRouter.get("/", async (_req, res) => {
+  try {
+    await fs.mkdir(PROJECTS_ROOT, { recursive: true });
+    const entries = await fs.readdir(PROJECTS_ROOT, { withFileTypes: true });
+    const projects = entries
+      .filter((e) => e.isDirectory() && !e.name.startsWith("."))
+      .map((e) => e.name)
+      .sort();
+    res.json({ projects });
+  } catch (err) {
+    res.status(500).json({ error: (err as Error).message });
+  }
+});
+
+projectsRouter.post("/:project", async (req, res) => {
+  const parsed = projectNameSchema.safeParse(req.params.project);
+  if (!parsed.success) {
+    res.status(400).json({ error: parsed.error.issues });
+    return;
+  }
+  const name = parsed.data;
+  const dir = path.join(PROJECTS_ROOT, name);
+  try {
+    await fs.mkdir(dir, { recursive: true });
+    const main = path.join(dir, "main.typ");
+    try {
+      await fs.access(main);
+    } catch {
+      await fs.writeFile(
+        main,
+        // The Typst heading `=` must be followed by a space, then the title.
+        `= ${name}\n\nHello from a fresh project.\n`,
+        "utf8",
+      );
+    }
+    res.status(201).json({ project: name });
+  } catch (err) {
+    res.status(500).json({ error: (err as Error).message });
+  }
+});
+
+projectsRouter.get("/:project", async (req, res) => {
+  const parsed = projectNameSchema.safeParse(req.params.project);
+  if (!parsed.success) {
+    res.status(400).json({ error: parsed.error.issues });
+    return;
+  }
+  const dir = projectDir(parsed.data);
+  try {
+    await fs.access(dir);
+  } catch {
+    res.status(404).json({ error: "project not found" });
+    return;
+  }
+  res.json({ project: parsed.data, uri: pathToFileURL(dir).href });
+});
+
+projectsRouter.get("/:project/tree", async (req, res) => {
+  const parsed = projectNameSchema.safeParse(req.params.project);
+  if (!parsed.success) {
+    res.status(400).json({ error: parsed.error.issues });
+    return;
+  }
+  const dir = projectDir(parsed.data);
+  try {
+    await fs.access(dir);
+  } catch {
+    res.status(404).json({ error: "project not found" });
+    return;
+  }
+  const out: { path: string; mtime: number }[] = [];
+  const budget = { left: MAX_TREE_ENTRIES };
+
+  async function walk(rel: string, depth: number): Promise<void> {
+    if (depth > MAX_TREE_DEPTH || budget.left <= 0) return;
+    const abs = path.join(dir, rel);
+    const entries = await fs.readdir(abs, { withFileTypes: true });
+    for (const entry of entries) {
+      if (budget.left <= 0) return;
+      if (entry.name.startsWith(".") || entry.name === "node_modules") continue;
+      const childRel = rel ? `${rel}/${entry.name}` : entry.name;
+      const childAbs = path.join(abs, entry.name);
+      const stat = await fs.stat(childAbs);
+      if (entry.isDirectory()) {
+        await walk(childRel, depth + 1);
+      } else if (entry.isFile() && entry.name.endsWith(".typ")) {
+        out.push({ path: childRel, mtime: stat.mtimeMs });
+        budget.left -= 1;
+      }
+    }
+  }
+
+  await walk("", 0);
+  res.json({ project: parsed.data, files: out });
+});