fix: wire up frontend build pipeline for Wails v2

- embed.go: embed index.html + all:src directly instead of all:dist,
  so `go build` works without a prior npm build step
- index.html: add missing xterm.css vendor stylesheet link
- build.js: add buildDist() to assemble dist/ with index.html and the
  full src/ tree; update required-file paths to match dist/ layout
- Add placeholder xterm lib stubs in src/js/lib/ and src/css/lib/ so
  the app can start before `npm install` is run
- .gitignore: stop ignoring the lib placeholder files so they are
  available on a fresh clone

frontend/scripts/build.js

@@ -1,13 +1,14 @@
 /**
  * build.js — Build script for the Nexus Terminal frontend.
  *
- * In production mode (no flags): copies assets and validates that all
- * required files are in place.
+ * In production mode (no flags): copies vendor assets, assembles the
+ * dist/ directory with all files needed by the Wails embed, and validates
+ * that every required file is present.
  *
- * In watch mode (--watch): copies assets, then watches for source changes
- * and prints a notification when files change. Wails dev mode handles the
- * actual live-reload; this script simply keeps the process alive so the
- * frontend:dev:watcher contract is satisfied.
+ * In watch mode (--watch): performs the same build, then watches for
+ * source changes and prints a notification when files change.  Wails dev
+ * mode handles the actual live-reload; this script simply keeps the
+ * process alive so the frontend:dev:watcher contract is satisfied.
  */
 'use strict';
 
@@ -16,29 +17,86 @@ const path = require('path');
 const { execSync } = require('child_process');
 
 const frontendDir = path.resolve(__dirname, '..');
+const distDir     = path.join(frontendDir, 'dist');
 const watchMode   = process.argv.includes('--watch');
 
-// Files that must exist after a successful build
+// Files that must exist after a successful build (relative to frontend/)
 const requiredFiles = [
   'dist/index.html',
-  'src/css/lib/xterm.css',
-  'src/js/lib/xterm.min.js',
-  'src/js/lib/xterm-addon-fit.min.js',
-  'src/js/lib/xterm-addon-search.min.js',
-  'src/js/lib/xterm-addon-web-links.min.js',
+  'dist/src/css/lib/xterm.css',
+  'dist/src/js/lib/xterm.min.js',
+  'dist/src/js/lib/xterm-addon-fit.min.js',
+  'dist/src/js/lib/xterm-addon-search.min.js',
+  'dist/src/js/lib/xterm-addon-web-links.min.js',
 ];
 
 /**
- * Runs the asset copy script to ensure library files are present.
+ * Recursively copies a directory tree, creating parents as needed.
+ */
+function copyDirSync(src, dest) {
+  fs.mkdirSync(dest, { recursive: true });
+  for (const entry of fs.readdirSync(src, { withFileTypes: true })) {
+    const srcPath  = path.join(src, entry.name);
+    const destPath = path.join(dest, entry.name);
+    if (entry.isDirectory()) {
+      copyDirSync(srcPath, destPath);
+    } else {
+      fs.copyFileSync(srcPath, destPath);
+    }
+  }
+}
+
+/**
+ * Removes a directory tree if it exists.
+ */
+function cleanDir(dir) {
+  if (fs.existsSync(dir)) {
+    fs.rmSync(dir, { recursive: true, force: true });
+  }
+}
+
+/**
+ * Runs the asset copy script to pull xterm files into src/js/lib/ and
+ * src/css/lib/.
  */
 function copyAssets() {
-  console.log('[build] Copying library assets…');
+  console.log('[build] Copying vendor library assets…');
   execSync('node scripts/copy-assets.js', {
     cwd:   frontendDir,
     stdio: 'inherit',
   });
 }
 
+/**
+ * Assembles the dist/ directory with everything the Wails embed needs:
+ *   dist/index.html
+ *   dist/src/css/  (application + lib stylesheets)
+ *   dist/src/js/   (application + lib scripts)
+ *   dist/src/components/  (if present)
+ *   dist/src/assets/      (if present)
+ */
+function buildDist() {
+  console.log('[build] Assembling dist/ directory…');
+
+  // Start fresh so stale files are removed
+  cleanDir(distDir);
+  fs.mkdirSync(distDir, { recursive: true });
+
+  // Copy the root index.html
+  fs.copyFileSync(
+    path.join(frontendDir, 'index.html'),
+    path.join(distDir, 'index.html'),
+  );
+
+  // Copy the entire src/ tree (CSS, JS, components, assets, lib files)
+  const srcDir = path.join(frontendDir, 'src');
+  if (fs.existsSync(srcDir)) {
+    copyDirSync(srcDir, path.join(distDir, 'src'));
+  }
+
+  console.log('[build] dist/ assembled.');
+}
+
 /**
  * Validates that every required file exists.
  * Returns true if all files are present.
@@ -67,7 +125,7 @@ function watch() {
   console.log(`[build] Watching ${srcDir} for changes…`);
 
   // Use fs.watch recursively where supported (macOS, Windows).
-  // On Linux, this falls back to non-recursive — acceptable for dev use.
+  // On Linux this falls back to non-recursive — acceptable for dev use.
   try {
     fs.watch(srcDir, { recursive: true }, (_event, filename) => {
       if (filename) {
@@ -77,7 +135,6 @@ function watch() {
     });
   } catch (err) {
     console.warn('[build] Recursive watch not supported; polling fallback.');
-    // Keep the process alive even if watch fails
   }
 
   // Prevent the process from exiting
@@ -93,6 +150,8 @@ try {
   process.exit(1);
 }
 
+buildDist();
+
 if (!validate()) {
   console.error('[build] Validation failed — some required files are missing.');
   process.exit(1);