fix(ci): install ruff before lint step

ruff is not in requirements.txt (dev-only tool) so the CI runner
couldn't find it. Install explicitly in the workflow.

.forgejo/workflows/ci.yml

@@ -29,6 +29,9 @@ jobs:
       - name: Install dependencies
         run: pip install -r requirements.txt
 
+      - name: Install lint tools
+        run: pip install ruff
+
       - name: Lint
         run: ruff check .