fix: 添加 Tauri v2 权限配置以支持文件对话框

新增文件:
- capabilities/default.json: Tauri v2 权限配置文件

权限配置:
- core🪟* - 窗口控制权限
- core:webview:* - Webview 权限
- shell:* - Shell 命令权限
- dialog:* - 文件对话框权限（包含 allow-open）
- fs:* - 文件系统权限

修复问题:
- 模型文件选择对话框无法打开
- Tauri v2 默认无权限，需要通过 capabilities 配置

构建结果:
- Linux GUI: dist/impress-asr-linux-x64-20260521_202605.tar.gz (4.8MB)
- 文件对话框现在可以正常打开

capabilities/default.json

@@ -0,0 +1,29 @@
+{
+  "$schema": "https://schema.tauri.app/v2/config/capability",
+  "identifier": "main",
+  "description": "Main capability for the application",
+  "windows": ["main"],
+  "permissions": [
+    "core:default",
+    "core:window:default",
+    "core:window:allow-show",
+    "core:window:allow-hide",
+    "core:window:allow-close",
+    "core:window:allow-set-focus",
+    "core:window:allow-start-dragging",
+    "core:webview:default",
+    "core:webview:allow-internal-toggle-devtools",
+    "shell:default",
+    "shell:allow-open",
+    "dialog:default",
+    "dialog:allow-open",
+    "dialog:allow-save",
+    "dialog:allow-message",
+    "dialog:allow-ask",
+    "dialog:allow-confirm",
+    "fs:default",
+    "fs:allow-read",
+    "fs:allow-write",
+    "fs:allow-exists"
+  ]
+}

gen/schemas/capabilities.json

@@ -1 +1 @@
-{}
+{"main":{"identifier":"main","description":"Main capability for the application","local":true,"windows":["main"],"permissions":["core:default","core:window:default","core:window:allow-show","core:window:allow-hide","core:window:allow-close","core:window:allow-set-focus","core:window:allow-start-dragging","core:webview:default","core:webview:allow-internal-toggle-devtools","shell:default","shell:allow-open","dialog:default","dialog:allow-open","dialog:allow-save","dialog:allow-message","dialog:allow-ask","dialog:allow-confirm","fs:default","fs:allow-read","fs:allow-write","fs:allow-exists"]}}