feat: Asahi validation tests, rootfs build fixes, shellcheck-clean scripts

- Add 16 validation tests: shellcheck (3 roles), installer_data.json
  schema (8), Python parser validation, ZIP structure (3), rootfs mount
- Fix empty SSH keys generating invalid bash (SC1073)
- Fix __dirname crash in ESM modules (use import.meta.url)
- Fix rootfs build: mkdir -p before writing, correct binary paths
- Add .gitignore for large build artifacts (.asahi-cache, *.zip)
- Bump smoke test timeout for additional static plugin registration

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

bastion/asahi-repo/installer_data.json

@@ -0,0 +1,47 @@
+{
+  "os_list": [
+    {
+      "name": "Fedora Asahi Lab (infra)",
+      "default_os_name": "Fedora Linux Lab",
+      "boot_object": "m1n1.bin",
+      "next_object": "m1n1/boot.bin",
+      "package": "fedora-asahi-lab.zip",
+      "supported_fw": [
+        "12.3",
+        "12.3.1",
+        "13.5"
+      ],
+      "partitions": [
+        {
+          "name": "EFI",
+          "type": "EFI",
+          "size": "524288000B",
+          "format": "fat",
+          "volume_id": "0x804be8a6",
+          "copy_firmware": true,
+          "copy_installer_data": true,
+          "source": "esp"
+        },
+        {
+          "name": "Boot",
+          "type": "Linux",
+          "size": "1073741824B",
+          "image": "boot.img"
+        },
+        {
+          "name": "Root",
+          "type": "Linux",
+          "size": "4626296832B",
+          "expand": false,
+          "image": "root.img"
+        },
+        {
+          "name": "Data",
+          "type": "Linux",
+          "size": "1073741824B",
+          "expand": true
+        }
+      ]
+    }
+  ]
+}