chore: stage all pending work — caption styling, media server, processing modal, docs, summaries

Includes:
- Extended caption styling (font, shadow, dimmed color, bg toggle)
- Media server, subtitle downloader, VTT parser, processing modal
- Waveform tiers, thumbnail/timeline improvements, transport controls
- Hybrid download model, dependency management, clip export enhancements
- 21 chat summaries, 2 implementation plans, 2 design specs

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

src-tauri/tauri.conf.json

@@ -21,7 +21,14 @@
       "csp": null,
       "assetProtocol": {
         "enable": true,
-        "scope": ["$TEMP/**", "$TMP/**", "/tmp/**"]
+        "scope": [
+          "$TEMP/**",
+          "$TMP/**",
+          "/tmp/**",
+          "/private/tmp/**",
+          "/private/var/**",
+          "/var/**"
+        ]
       }
     }
   },