fix(ci): run Renovate via official Docker image

`renovatebot/github-action@v40` failed to resolve on Gitea Actions
with `reference not found` when act_runner attempted the go-git
clone. Whether the issue is a missing major-rolling tag upstream or
a go-git tag-fetch quirk, the wrapper action is the wrong layer to
fight: it just shells out to the same `renovate/renovate` image we
can run ourselves.

Switch to a direct `docker run renovate/renovate:40` invocation:

- decouples from third-party action-tag resolution;
- pins the Renovate runtime version explicitly (reproducible);
- one fewer indirection to debug.

The job container already has access to the host Docker daemon
(per ci-runners.compose.yml mounting /var/run/docker.sock), so the
sibling `docker run` works out of the box. Renovate clones the
target repo itself using the API token, so no `actions/checkout`
or host bind-mount is needed.

.gitea/workflows/renovate.yml

@@ -6,6 +6,18 @@
 # repo root. This workflow only controls *when* Renovate runs and how
 # it authenticates against Gitea.
 #
+# Implementation note — we run the official `renovate/renovate` Docker
+# image directly via `docker run` rather than the `renovatebot/github-
+# action` wrapper. The wrapper relies on act_runner being able to
+# resolve arbitrary GitHub tags via go-git, which is brittle (we hit
+# `reference not found` on `@v40`). Going straight to the image:
+#  * decouples from action-tag resolution issues;
+#  * pins the Renovate runtime version explicitly (reproducible);
+#  * one fewer layer of indirection to debug.
+#
+# Renovate clones the repo itself using RENOVATE_TOKEN — no
+# `actions/checkout` step, no host bind-mount needed.
+#
 # Authentication: a Gitea Personal Access Token issued for the dedicated
 # `apf-portal-bot` user, stored as the RENOVATE_TOKEN secret. The full
 # bot-onboarding procedure lives in docs/development.md → "Dependency
@@ -26,12 +38,22 @@ jobs:
   renovate:
     runs-on: [self-hosted, on-prem]
     steps:
-      - uses: renovatebot/github-action@v40
+      - name: Run Renovate
-        with:
+        # Pin to the major; the bot will propose its own bumps once
-          token: ${{ secrets.RENOVATE_TOKEN }}
+        # it is healthy (Renovate self-updates the workflow files it
-          configurationFile: renovate.json
+        # finds in the repo it manages).
+        run: |
+          docker run --rm \
+            --name "renovate-${{ github.run_id }}" \
+            -e RENOVATE_TOKEN \
+            -e RENOVATE_PLATFORM \
+            -e RENOVATE_ENDPOINT \
+            -e RENOVATE_AUTODISCOVER \
+            -e RENOVATE_REPOSITORIES \
+            -e LOG_LEVEL \
+            renovate/renovate:40
         env:
-          # Tell Renovate this is Gitea, not GitHub.
+          RENOVATE_TOKEN: ${{ secrets.RENOVATE_TOKEN }}
           RENOVATE_PLATFORM: gitea
           # Gitea API endpoint — derived from the workflow's own server
           # URL so a Gitea → GitLab migration only requires changing