docs: update comments and README to reflect current feature set

- Refresh app.py module and route docstrings for runtime settings,
  MP3 tagging, rate limiting, revision workflow, and admin actions.
- Clarify config.py and models.py comments.
- Update template comments/CSS for dashboard filters, request detail,
  player page, and settings page.
- Rewrite README.md with current features, status flow, file layout,
  deployment variables, and troubleshooting.
- Refresh REVIEW.md quick-reference.
- Add MAX_REVISIONS to docker-compose.yml environment list.
- Expand requirements.txt comment coverage.

No version history or changelog included.

docker-compose.yml

@@ -28,6 +28,7 @@ services:
       - PUBLIC_BASE_URL=${PUBLIC_BASE_URL}
       - BOOTH_NAME=${BOOTH_NAME:-Trollgorithm Theme Songs}
       - INTERNAL_PORT=${INTERNAL_PORT:-8000}
+      - MAX_REVISIONS=${MAX_REVISIONS:-2}
       - PRICE_PER_VERSION=${PRICE_PER_VERSION:-10.00}
       - CURRENCY=${CURRENCY:-CAD}
       - DATABASE=${DATABASE:-/app/data/booth.db}