feat(release): add cross-platform packaging

Add target-aware engine provisioning, platform package configs, and CI/release verification for macOS arm64, Windows x64, and Linux AppImage.

scripts/smoke-packaged-app.js

@@ -0,0 +1,62 @@
+#!/usr/bin/env node
+import { spawn } from 'node:child_process';
+import path from 'node:path';
+
+function argValue(name) {
+  const index = process.argv.indexOf(name);
+  return index >= 0 ? process.argv[index + 1] : undefined;
+}
+
+const executableArg = argValue('--executable');
+if (!executableArg) {
+  console.error('Pass --executable <path>.');
+  process.exit(1);
+}
+const executable = path.resolve(executableArg);
+
+const child = spawn(executable, [], {
+  cwd: process.env.RUNNER_TEMP || process.env.TMPDIR || process.cwd(),
+  detached: process.platform !== 'win32',
+  stdio: ['ignore', 'pipe', 'pipe']
+});
+let stderr = '';
+let spawnError = null;
+child.on('error', error => {
+  spawnError = error;
+});
+child.stderr.on('data', data => {
+  stderr += data.toString();
+});
+
+let readyPort = null;
+for (let attempt = 0; attempt < 40 && readyPort === null; attempt += 1) {
+  for (let port = 6412; port <= 6422; port += 1) {
+    try {
+      const response = await fetch(`http://127.0.0.1:${port}/ping`);
+      if (response.headers.get('x-firelink-server') === '1') {
+        readyPort = port;
+        break;
+      }
+    } catch {}
+  }
+  if (readyPort === null) {
+    await new Promise(resolve => setTimeout(resolve, 250));
+  }
+}
+
+if (process.platform === 'win32') {
+  spawn('taskkill', ['/pid', String(child.pid), '/t', '/f'], { stdio: 'ignore' });
+} else {
+  try {
+    process.kill(-child.pid, 'SIGTERM');
+  } catch {
+    child.kill('SIGTERM');
+  }
+}
+
+if (readyPort === null) {
+  const detail = spawnError?.message || stderr.slice(-1000);
+  console.error(`Packaged Firelink did not expose extension server. ${detail}`);
+  process.exit(1);
+}
+console.log(`Packaged Firelink smoke passed on 127.0.0.1:${readyPort}`);