Add embedded audio/subtitle track selection for multi-track files

Files with multiple embedded tracks (e.g. MKV from media sources or
downloads) previously exposed none of them: mpv's track-list was never
read, aid was never set, and sid was only ever no/auto. The quality
selector showed no Audio or Subtitles tab for such files.

MPVClient now observes track-list/aid/sid and delivers a coalesced,
leniently decoded [MPVTrack] snapshot; selection state is derived from
the reported "selected" flags. Embedded tracks are switched live via
aid/sid (no reload), surfaced in the existing Audio/Subtitles sections
alongside external captions on iOS, tvOS and macOS. External sub-add/
audio-add tracks are filtered out to avoid double-listing. User picks
are sticky across same-video reloads (quality switch, audio mode,
retries) and preferred audio/subtitle languages auto-select a matching
embedded track once per load, with external captions taking precedence.

Yattee/Localizable.xcstrings

@@ -7886,6 +7886,39 @@
         }
       }
     },
+    "player.track.default" : {
+      "comment" : "Badge for the container's default embedded track",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "DEFAULT"
+          }
+        }
+      }
+    },
+    "player.track.forced" : {
+      "comment" : "Badge for forced embedded subtitle tracks",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "FORCED"
+          }
+        }
+      }
+    },
+    "player.track.number %lld" : {
+      "comment" : "Fallback name for an embedded track without title or language",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Track %lld"
+          }
+        }
+      }
+    },
     "player.tvos.volumeDown" : {
       "extractionState" : "stale",
       "localizations" : {