build(deps): pin a reproducible lock + pip-audit; bump node 20->22 (E1 S4, SEC-5/DX-3)

requirements.txt stays the source (floor ranges); requirements.lock pins the
exact resolved versions (generated in the python:3.12-slim prod base, extras like
psycopg-binary/uvloop included). The prod Dockerfile, Dockerfile.test and CI now
install the lock, so the image is reproducible and the versions are the ones
pip-audit scans. CI gains a non-blocking pip-audit step over the lock. The
frontend build + CI move from the EOL node 20 to node 22.

backend/requirements.lock

@@ -0,0 +1,57 @@
+# Pinned dependency lock for reproducible builds (SEC-5). GENERATED — do not hand-edit.
+# Source of truth is requirements.txt (the floor ranges); regenerate after editing it with:
+#   docker run --rm -v "$PWD":/b python:3.12-slim sh -c 'pip install -q -r /b/requirements.txt && pip freeze --exclude pip --exclude setuptools --exclude wheel' | sort
+# The prod Dockerfile + Dockerfile.test + CI install THIS file; pip-audit scans it in CI.
+APScheduler==3.11.3
+Authlib==1.7.2
+Mako==1.4.1
+MarkupSafe==3.0.3
+PyYAML==6.0.3
+SQLAlchemy==2.0.52
+alembic==1.19.1
+annotated-doc==0.0.5
+annotated-types==0.8.0
+anyio==4.14.2
+argon2-cffi-bindings==25.1.0
+argon2-cffi==25.1.0
+bgutil-ytdlp-pot-provider==1.3.1
+brotli==1.2.0
+certifi==2026.7.22
+cffi==2.1.1
+charset-normalizer==3.5.1
+click==8.4.2
+cryptography==46.0.7
+fastapi==0.141.1
+feedparser-sgmllib==2.1.0
+feedparser==6.0.14
+greenlet==3.5.5
+h11==0.16.0
+httpcore==1.0.9
+httptools==0.8.0
+httpx==0.28.1
+idna==3.18
+itsdangerous==2.2.0
+joserfc==1.7.4
+mutagen==1.48.1
+numpy==2.5.2
+psycopg-binary==3.3.4
+psycopg==3.3.4
+py3langid==0.3.0
+pycparser==3.0
+pycryptodomex==3.23.0
+pydantic-settings==2.15.0
+pydantic==2.13.4
+pydantic_core==2.46.4
+python-dotenv==1.2.3
+requests==2.34.2
+starlette==1.6.0
+typing-inspection==0.4.4
+typing_extensions==4.16.0
+tzlocal==5.4.4
+urllib3==2.7.0
+uvicorn==0.52.3
+uvloop==0.22.1
+watchfiles==1.2.0
+websockets==17.0.1
+yt-dlp-ejs==0.8.0
+yt-dlp==2026.7.4