feat: migrate backend to uv package manager

Replace pip + requirements.txt with uv for dependency management.

- Multi-stage Dockerfile using ghcr.io/astral-sh/uv builder image
- CI updated to use astral-sh/setup-uv@v4
- Ruff config moved to [tool.ruff.lint] (fixes deprecation)
- Transitive deps removed, missing direct deps added (requests, PySocks, urllib3)
- Database layer migrated to async (AsyncSession + aiosqlite)
- Tests updated to match async database interface

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/build.yml

@@ -13,20 +13,15 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - name: Set up Python 3.11
-        uses: actions/setup-python@v3
+      - uses: astral-sh/setup-uv@v4
         with:
-          python-version: '3.11'
+          version: "latest"
       - name: Install dependencies
-        run: |
-          python -m pip install --upgrade pip
-          if [ -f backend/requirements.txt ]; then pip install -r backend/requirements.txt; fi
-          pip install pytest
+        run: cd backend && uv sync --group dev
       - name: Test
-        working-directory: ./backend/src
         run: |
-          mkdir -p config
-          pytest
+          mkdir -p backend/config
+          cd backend && uv run pytest src/test -v
 
   webui-test:
     runs-on: ubuntu-latest
@@ -295,10 +290,6 @@ jobs:
           echo ${{ needs.version-info.outputs.version }}
           echo "VERSION='${{ needs.version-info.outputs.version }}'" >> module/__version__.py
 
-      - name: Copy requirements.txt
-        working-directory: ./backend
-        run: cp requirements.txt src/requirements.txt
-
       - name: Zip app
         run: |
           cd backend && zip -r app-v${{ needs.version-info.outputs.version }}.zip src