feat(notifications): add overlay notifications with position config

- Add Catppuccin Macchiato overlay notification stack with 3s transient timeout
- Add `notifications.overlayPosition` config (top-left | top | top-right)
- Route startup tokenization and subtitle annotation status through configured surfaces
- Deduplicate rapid subtitle mode toggle notifications
- Change `both` to mean overlay + system; add `osd-system` as legacy alias for old behavior
- Keep `osd`/`osd-system` as config-file-only legacy values; Settings UI offers overlay/system/both/none

docs-site/anki-integration.md

@@ -216,11 +216,13 @@ Animated AVIF requires an AV1 encoder (`libaom-av1`, `libsvtav1`, or `librav1e`)
     "overwriteImage": true,         // replace existing image, or append
     "mediaInsertMode": "append",    // "append" or "prepend" to field content
     "autoUpdateNewCards": true,     // auto-update when new card detected
-    "notificationType": "osd"       // "osd", "system", "both", or "none"
+    "notificationType": "overlay"   // "overlay", "system", "both", or "none"
   }
 }
 ```
 
+`both` now means overlay + system notification. `osd` and `osd-system` are legacy config-file-only values; set `notificationType` to `"osd-system"` in `config.jsonc` if you previously used `both` and want to keep mpv OSD + system notifications. The Settings window shows `osd` or `osd-system` when already configured, but only offers `overlay`, `system`, `both`, and `none` as normal choices.
+
 `overwriteAudio` applies to automatic card updates and duplicate-card enrichment. Manual clipboard subtitle updates (`Ctrl/Cmd+C`, then `Ctrl/Cmd+V`) always replace generated sentence audio, while leaving the word audio field unchanged.
 
 ## AI Translation
@@ -351,7 +353,7 @@ When you mine the same word multiple times, SubMiner can merge the cards instead
       "overwriteImage": true,
       "mediaInsertMode": "append",
       "autoUpdateNewCards": true,
-      "notificationType": "osd",
+      "notificationType": "overlay",
     },
     "ai": {
       "enabled": false,