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.

src-tauri/tauri.linux.conf.json

@@ -0,0 +1,18 @@
+{
+  "app": {
+    "windows": [
+      {
+        "title": "Firelink",
+        "width": 1280,
+        "height": 760,
+        "minWidth": 960,
+        "minHeight": 640,
+        "transparent": false,
+        "decorations": true
+      }
+    ]
+  },
+  "bundle": {
+    "targets": ["appimage"]
+  }
+}