Wire watch history, resume positions and persistent queue

WatchPage now records every played video in watch_history, saves the
playback position every 5 seconds and on stop/end (completed at >=95%),
and seeks back on replay when player.resume is "auto" - resume kicks in
between 30 seconds and 95% of the duration. The play queue persists
across restarts and reorders/removals write through immediately; the
main window's closeEvent flushes position and queue and releases libmpv.

PlayerPanel gains an automatic stall-retry: YouTube's CDN intermittently
serves stalled streams to non-browser clients (reproduced ~1/3 of
attempts headless with identical code), and a reload re-resolves onto a
healthy node - two retries after 25s of no playback, then a user-facing
error.

ytsage_constants now prepends the managed-binaries dir to PATH so
yt-dlp subprocesses (including mpv's ytdl_hook) can find the managed
Deno runtime - previously nothing exported APP_BIN_DIR, so the deno
integration silently never worked.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ytsage/utils/ytsage_constants.py

@@ -238,3 +238,13 @@ else:
             YTDLP_APP_BIN_PATH.parent.mkdir(parents=True, exist_ok=True)
         if "DENO_APP_BIN_PATH" in globals():
             DENO_APP_BIN_PATH.parent.mkdir(parents=True, exist_ok=True)
+
+    # Put the managed-binaries dir on PATH for this process and all children:
+    # yt-dlp locates the Deno JS runtime (nsig/PO-token challenges) via PATH,
+    # and nothing else ever exports APP_BIN_DIR.
+    _bin_dirs = {str(APP_BIN_DIR)}
+    if "DENO_APP_BIN_PATH" in globals():
+        _bin_dirs.add(str(DENO_APP_BIN_PATH.parent))
+    for _bin_dir in _bin_dirs:
+        if _bin_dir not in os.environ.get("PATH", "").split(os.pathsep):
+            os.environ["PATH"] = _bin_dir + os.pathsep + os.environ.get("PATH", "")