fix: use per-video caption cache dir to prevent cross-video caption bleed

Subtitle downloads were going to a shared /tmp/video-clipper/subtitles/ dir,
so find_vtt_file could return captions from a previously-loaded video. Now
uses cache_manager::caption_cache_dir (URL-hash-keyed) with pre-download
cleanup, matching the existing per-video caching pattern.

Bump to v0.2.2.

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

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "gui-video-clipper",
-  "version": "0.2.0",
+  "version": "0.2.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "gui-video-clipper",
-      "version": "0.2.0",
+      "version": "0.2.1",
       "license": "MIT",
       "dependencies": {
         "@lucide/svelte": "^1.47.0",