Migrate dependency management to uv

Replace requirements.txt with pyproject.toml (direct deps only; uv
resolves the rest into uv.lock). Point the systemd unit at the
uv-managed .venv, and gitignore it.

Run `uv lock` to generate the lockfile and commit it.

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

deploy/food.service

@@ -7,9 +7,9 @@ Type=notify
 User=openclaw
 Group=openclaw
 WorkingDirectory=/var/lib/food
-Environment="PATH=/var/lib/food/venv/bin:/usr/bin"
+Environment="PATH=/var/lib/food/.venv/bin:/usr/bin"
 Environment="DJANGO_SETTINGS_MODULE=food_project.settings"
-ExecStart=/var/lib/food/venv/bin/gunicorn food_project.wsgi:application \
+ExecStart=/var/lib/food/.venv/bin/gunicorn food_project.wsgi:application \
     --bind 127.0.0.1:8042 \
     --workers 2 \
     --timeout 30 \