chore(fc2a): move ruff version ownership to the runner image

Per FabledRulebook forgejo.md, toolchain versions live on the runner
image, not in the workflow. Two changes here, paired with the runner
image bump (RUFF_VERSION 0.9.7 -> 0.15.13 in CI-Runner/CI-python):

- Drop "ruff>=0.9,<1.0" from ci.yml's pip install — the runner image's
  pre-installed ruff is authoritative now. Previously this constraint
  matched the existing 0.9.7 in the image so pip never upgraded.
- Flip ruff.toml's target-version back to py314 now that the runner
  has a ruff new enough to know about it.

Next bump path: edit RUFF_VERSION in CI-Runner/CI-python/Dockerfile,
'make push', done. No workflow churn.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.forgejo/workflows/ci.yml

@@ -44,7 +44,10 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Python deps
-        run: pip install -r requirements.txt pytest pytest-asyncio "ruff>=0.9,<1.0"
+        # ruff is pre-installed in the python-ci runner image (see
+        # CI-Runner/CI-python/Dockerfile's RUFF_VERSION). Per FabledRulebook
+        # forgejo.md, toolchain versions live on the runner image, not here.
+        run: pip install -r requirements.txt pytest pytest-asyncio
 
       - name: Ruff lint
         run: ruff check backend/ tests/ alembic/