fix(cookies): mount youtube/instagram cookies from host instead of baking into image

Cookies baked into the image (COPY . .) required a full CI/CD rebuild
to refresh, incompatible with the cron job on the fedora machine that
re-extracts cookies from a logged-in browser every 20 minutes and
scp's them to prod. Volume-mount the cookies file instead — yt-dlp
reads it from disk per request, so a fresh scp takes effect
immediately with no container restart. The image-baked copy still
exists as a build-time fallback.

Also refresh the committed cookies snapshot (the cron's source yt-dlp
turned out to be missing on the fedora box, so prior commits had been
carrying years-stale cookies without anyone noticing).

docker-compose.prod.yml

@@ -39,6 +39,7 @@ services:
     restart: unless-stopped
     volumes:
       - ./youtube-downloads:/app/downloads
+      - ./youtube_cookies.txt:/app/youtube_cookies.txt
     environment:
       - YOUTUBE_COOKIES_FILE=/app/youtube_cookies.txt
       - PORT=5557
@@ -51,6 +52,7 @@ services:
     network_mode: host
     volumes:
       - ./instagram-downloads:/app/downloads
+      - ./instagram_cookies.txt:/app/instagram_cookies.txt
     environment:
       - INSTAGRAM_COOKIES_FILE=/app/instagram_cookies.txt
       - PORT=5556