feat: report authoritative playback progress from shared backend

Sources/Core/player.h

@@ -37,6 +37,13 @@ typedef struct PlayerState {
 // Playback commands are asynchronous. False means invalid input or a full command queue.
 // Paths are copied before returning. All other calls require a live handle.
 Player *player_create(void);
+// Opt-in reporting must be initialized before opening media. Creates a new 0600
+// file exclusively; errors never change playback state. Error buffers hold 512 bytes.
+bool player_set_progress_file(Player *player, const char *path, char *error);
+bool player_get_progress_error(Player *player, char *error);
+// Stops the worker and drains final reporting, allowing errors to be shown before
+// destroying the handle. Idempotent; do not call from an audio callback.
+bool player_shutdown(Player *player, char *progress_error);
 typedef struct PlayerNetworkSource {
     // Primary video or combined audio/video HTTP(S) URL; audio_url is optional.
     const char *video_url;
@@ -46,6 +53,12 @@ typedef struct PlayerNetworkSource {
     const char *audio_headers;
     double duration;
     bool is_live;
+    // Canonical YouTube webpage identity, never an extracted stream URL.
+    // NULL/empty means no reporting for this source.
+    const char *media_url;
+    // Initial restored position, applied before publishing ready state. Zero
+    // starts at the beginning; out-of-duration bookmarks also start at zero.
+    double initial_position;
 } PlayerNetworkSource;
 bool player_open(Player *player, const char *path);
 // Streams directly; never downloads or muxes the entire media file before opening.