YouTube regularly breaks older yt-dlp versions. Bumped the minimum version
and added a separate Docker layer for yt-dlp so it can be upgraded without
busting the main pip cache.
Cache-first was preventing updates from reaching users. Network-first
always fetches fresh content and only falls back to cache when offline.
Also bumps cache version to evict stale cache-first entries.
Adds a Settings panel to upload a cookies.txt file directly from the
browser, persisted in a named Docker volume. yt-dlp uses the file
when present to bypass YouTube bot detection.
