feat(devops): add renovate.yml runner workflow (digest-pinned, daily cron)

Daily schedule (0 3 * * *) cuts OSV-alert latency to ≤1 day. Pinned to
renovatebot/github-action@8217b3fc (v46.1.15) with renovate-version fixed
to "46.1.15" — matches the repo's pin-everything posture (ADR-041).

Token wired via RENOVATE_TOKEN secret (contents+pull_request+issues scopes
on dedicated bot account). Platform/endpoint injected via env so renovate.json
stays purely dependency-rule-scoped.

Closes part of #818.

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

.gitea/workflows/renovate.yml

@@ -0,0 +1,44 @@
+name: Renovate
+
+# Runs Renovate daily to surface newly-published advisories via OSV.dev
+# (osvVulnerabilityAlerts) and open routine update PRs on a weekly batch
+# schedule (see renovate.json §schedule). Security/vulnerability PRs are
+# raised immediately regardless of the weekly schedule window.
+#
+# Required Gitea secrets (see docs/adr/041-renovate-runner-setup.md):
+#   RENOVATE_TOKEN  — PAT with scopes: contents + pull_request + issues
+#                     Belongs to a dedicated bot account. Branch protection
+#                     on main must forbid this bot pushing directly.
+#
+# Platform config is injected via env vars below; the renovate.json in the
+# repo root carries only dependency rules (no platform/endpoint/repos).
+#
+# Digest pin: renovatebot/github-action@8217b3fc286df088d7c27f3255fe8414463bc0fd
+# corresponds to release v46.1.15. Update by bumping both the digest and the
+# renovate-version when Renovate publishes a new release. Renovate itself
+# will open a PR to bump this digest once it runs.
+
+on:
+  schedule:
+    - cron: "0 3 * * *"  # daily at 03:00 UTC — cuts OSV-alert latency to ≤1 day
+  workflow_dispatch:
+
+jobs:
+  renovate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Run Renovate
+        # Pinned by digest — this action holds contents+pull_request+issues
+        # scopes; an unpinned tag is a supply-chain risk (see ADR-041).
+        uses: renovatebot/github-action@8217b3fc286df088d7c27f3255fe8414463bc0fd  # v46.1.15
+        with:
+          configurationFile: renovate.json
+          token: ${{ secrets.RENOVATE_TOKEN }}
+          renovate-version: "46.1.15"
+        env:
+          RENOVATE_PLATFORM: gitea
+          RENOVATE_ENDPOINT: https://git.raddatz.cloud
+          RENOVATE_REPOSITORIES: '["marcel/familienarchiv"]'
+          LOG_LEVEL: info