feat: Asahi rootfs build pipeline + serve from bastion

- Add scripts/build-asahi-rootfs.sh: downloads upstream Fedora Asahi
  Remix Server, injects lab firstboot script + systemd service + SSH
  keys, repackages with installer_data.json that adds LVM Data partition
- Bastion serves built artifacts at /asahi/repo/* via fastify-static
- installer_data.json prefers built config, falls back to minimal
- Fix __dirname crash in ESM module (use import.meta.url)
- Fix smoke test timeout (was crashing due to __dirname)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bastion/src/cli/tests/smoke-bastion.test.ts

@@ -137,7 +137,7 @@ describe("bastion smoke tests", () => {
 
     // Wait for the server to start (look for the banner)
     const startedAt = Date.now();
-    const maxWait = 10_000;
+    const maxWait = 15_000;
     while (Date.now() - startedAt < maxWait) {
       if (stdout.includes("Waiting for PXE boot requests")) break;
       await sleep(200);