fix: about dialog, cache paths, keyframes, reprocess always uses low-res

- Replace native macOS About menu with custom Svelte dialog via Tauri event
- Inline SVG icon in AboutDialog (fixes broken image in webview)
- Align cache directory with Tauri $APPDATA, add to asset protocol scope
- Fix ffprobe 8.x keyframe parsing (skip_frame nokey, flexible parser)
- Copy caption files into cache dir when outside cache path
- Add -y flag to ffmpeg thumbnail extraction (prevent hang on re-extract)
- Reprocess always uses preview (low-res) file, never HQ export
- Prefer cached preview file for analysis even when HQ is cached
- Guard upgrade toast when already on HQ

Co-authored-by: Cursor <cursoragent@cursor.com>

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "gui-video-clipper",
-  "version": "0.1.0",
+  "version": "0.1.2",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "gui-video-clipper",
-      "version": "0.1.0",
+      "version": "0.1.2",
       "license": "MIT",
       "dependencies": {
         "@tauri-apps/api": "^2",