chore: YTM source — mount cookies volume; bump mcma-backend + mcma-webui

docker-compose.yml mounts ./data/youtube on api+worker for an optional yt-dlp cookies.txt; .env.example documents YOUTUBE_COOKIES_PATH. Bumps the backend + webui submodules to the YTM search/download feature commits. (mcma-bootstrap stays untracked — separate repo.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.yml

@@ -58,6 +58,7 @@ services:
       - /app/.venv # keep the image's venv, don't shadow it
       - ./data/media:/data/media
       - ./data/transcode-cache:/data/transcode-cache
+      - ./data/youtube:/data/youtube # yt-dlp cookies.txt (optional; see .env)
     ports:
       - "${API_PORT:-8000}:8000" # direct access for debugging / docs
     depends_on:
@@ -79,6 +80,7 @@ services:
       - /app/.venv
       - ./data/media:/data/media
       - ./data/transcode-cache:/data/transcode-cache
+      - ./data/youtube:/data/youtube # yt-dlp cookies.txt (optional; see .env)
     depends_on:
       db: { condition: service_healthy }
       redis: { condition: service_healthy }