feat(openfang): add bundled OpenFang runtime support

- Add prepare-openfang-runtime.mjs script for cross-platform binary download
- Update lib.rs to support binary runtime (fallback to Node.js for legacy)
- Add openfang.cmd/sh launcher scripts
- Update runtime-manifest.json for binary-based runtime
- Add README documentation for bundled runtime architecture

OpenFang binary is downloaded during build, supporting:
- Windows x64/ARM64 (.zip)
- macOS Intel/Apple Silicon (.tar.gz)
- Linux x64/ARM64 (.tar.gz)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src-tauri/tauri.conf.json

@@ -1,8 +1,8 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
-  "productName": "desktop",
-  "version": "0.1.0",
-  "identifier": "com.szend.desktop",
+  "productName": "ZClaw",
+  "version": "0.2.0",
+  "identifier": "com.zclaw.desktop",
   "build": {
     "beforeDevCommand": "pnpm dev",
     "devUrl": "http://localhost:1420",
@@ -12,9 +12,11 @@
   "app": {
     "windows": [
       {
-        "title": "desktop",
-        "width": 800,
-        "height": 600
+        "title": "ZClaw - OpenFang Desktop",
+        "width": 1200,
+        "height": 800,
+        "minWidth": 900,
+        "minHeight": 600
       }
     ],
     "security": {
@@ -23,7 +25,11 @@
   },
   "bundle": {
     "active": true,
-    "targets": "all",
+    "targets": "nsis",
+    "useLocalToolsDir": true,
+    "resources": [
+      "resources/openfang-runtime/"
+    ],
     "icon": [
       "icons/32x32.png",
       "icons/128x128.png",