Fix SABR backoff stalling playback & improve error logging

[Copilot]

YouTube's "locker" script defines isInlinePlaybackNoAd as non-writable/non-configurable, so direct assignment silently fails — the flag never reaches the request, triggering server-side SABR backoff that stalls playback after ~30 seconds. Error logs were also emitting [object Object] instead of readable output.

Changes

src/hooks/json-stringify.ts — bypass property locker

Instead of mutating YouTube's object in place, rebuild the holder → playbackContext → contentPlaybackContext chain with fresh plain objects via spread. JSON.stringify only serializes own enumerable properties, so the spread drops locked descriptors and lets the flag stick.

// Before — silently fails against locked descriptor
(ctx as Record<string, unknown>).isInlinePlaybackNoAd = true;

// After — fresh objects, no locked descriptors
value = {
  ...holder,
  playbackContext: {
    ...pbCtx,
    contentPlaybackContext: { ...ctx, isInlinePlaybackNoAd: true }
  }
};

src/playback-error-handler.ts — readable error logs

Use JSON.stringify on logged objects so the output is inspectable JSON rather than [object Object]. handlePlaybackError now includes videoId, title, full playerState, and videoError in one structured line.

src/player_api/yt-api.ts

Added title to the VideoData interface to surface it in error logs.