fix(ci): use uv pip install --system instead of uv sync

The act_runner containers don't support uv sync virtual environments
properly. Using --system installs directly into the system Python,
making all tools available on PATH.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -31,10 +31,10 @@ jobs:
         run: pip install uv
 
       - name: Install dependencies
-        run: uv sync --frozen
+        run: uv pip install --system -r requirements.txt -r requirements-dev.txt
 
       - name: Run ruff
-        run: uv run ruff check .
+        run: ruff check .
 
   # ---------------------------------------------------------------------------
   # Tests
@@ -67,24 +67,14 @@ jobs:
         with:
           python-version: ${{ env.PYTHON_VERSION }}
 
-      - name: Cache pip & venv
-        uses: actions/cache@v4
-        with:
-          path: |
-            ~/.cache/pip
-            .venv
-          key: ${{ runner.os }}-pip-${{ hashFiles('uv.lock', 'pyproject.toml') }}
-          restore-keys: |
-            ${{ runner.os }}-pip-
-
       - name: Install uv
         run: pip install uv
 
       - name: Install dependencies
-        run: uv sync --frozen
+        run: uv pip install --system -r requirements.txt -r requirements-test.txt
 
       - name: Run tests
-        run: uv run python -m pytest tests/ -v --tb=short
+        run: python -m pytest tests/ -v --tb=short
 
   architecture:
     runs-on: ubuntu-latest
@@ -102,10 +92,10 @@ jobs:
         run: pip install uv
 
       - name: Install dependencies
-        run: uv sync --frozen
+        run: uv pip install --system -r requirements.txt
 
       - name: Validate architecture
-        run: uv run python scripts/validate/validate_architecture.py
+        run: python scripts/validate/validate_architecture.py
 
   # ---------------------------------------------------------------------------
   # Security (non-blocking)
@@ -140,10 +130,10 @@ jobs:
         run: pip install uv
 
       - name: Install dependencies
-        run: uv sync --frozen
+        run: uv pip install --system -r requirements.txt -r requirements-dev.txt
 
       - name: Run audit
-        run: uv run python scripts/validate/validate_audit.py
+        run: python scripts/validate/validate_audit.py
 
   # ---------------------------------------------------------------------------
   # Build (docs - only on push to master)
@@ -163,10 +153,10 @@ jobs:
         run: pip install uv
 
       - name: Install dependencies
-        run: uv sync --frozen
+        run: uv pip install --system -r requirements.txt -r requirements-docs.txt
 
       - name: Build docs
-        run: uv run mkdocs build
+        run: mkdocs build
 
       - name: Upload docs artifact
         uses: actions/upload-artifact@v4