ci: run gates with .venv/bin directly

'uv run' re-syncs the project environment and rebuilds it on the system
interpreter, dropping uv-pip-installed tools like ruff. Invoke the venv
binaries directly so the matrix interpreter and installed tools are
exactly what runs.

Author: xxg1413

.github/workflows/validate.yml

@@ -39,25 +39,25 @@ jobs:
           uv pip install -r requirements-dev.lock.txt ruff
 
       - name: Lint with ruff
-        run: uv run ruff check .
+        run: .venv/bin/ruff check .
 
       - name: Run tests
-        run: uv run python -m pytest
+        run: .venv/bin/python -m pytest
 
       - name: Validate catalog
-        run: uv run python tools/validate_catalog.py
+        run: .venv/bin/python tools/validate_catalog.py
 
       - name: Verify public JSON exports
-        run: uv run python tools/export_catalog.py --check --target both
+        run: .venv/bin/python tools/export_catalog.py --check --target both
 
       - name: Verify browsable README indexes
-        run: uv run python tools/render_readmes.py --check
+        run: .venv/bin/python tools/render_readmes.py --check
 
       - name: Verify first-party content manifest
-        run: uv run python tools/build_content_manifest.py --check
+        run: .venv/bin/python tools/build_content_manifest.py --check
 
       - name: Verify runnable examples
-        run: uv run python tools/verify_examples.py
+        run: .venv/bin/python tools/verify_examples.py
 
       - name: Verify course folders
-        run: uv run python tools/verify_courses.py
+        run: .venv/bin/python tools/verify_courses.py