feat(renovate): add self-hosted Renovate config and Gitea Actions workflow

Run the pinned renovate/renovate image on the host runner every weekday at
04:17 (plus workflow_dispatch) against the gitea platform, authenticating with
the renovate-bot RENOVATE_TOKEN Actions secret. Minor and patch updates are
grouped and automerged only after CI passes; majors wait for dashboard
approval. Document the bot, secret rotation and the minimumReleaseAge policy in
the error-centre runbook.

.gitea/workflows/renovate.yaml

@@ -0,0 +1,42 @@
+name: Renovate
+
+on:
+  schedule:
+    - cron: "17 4 * * 1-5"
+  workflow_dispatch:
+    inputs:
+      debug:
+        description: "Debug-loglevel"
+        type: boolean
+        default: false
+
+# Niet overlappen met zichzelf; een tweede start wacht tot de eerste klaar is.
+concurrency:
+  group: renovate
+  cancel-in-progress: false
+
+env:
+  RENOVATE_VERSION: 44.164.10 # renovate: datasource=npm depName=renovate
+
+jobs:
+  renovate:
+    runs-on: ubuntu-latest
+    timeout-minutes: 60
+    steps:
+      - name: Run Renovate
+        env:
+          RENOVATE_TOKEN: ${{ secrets.RENOVATE_TOKEN }}
+          LOG_LEVEL: ${{ github.event.inputs.debug == 'true' && 'debug' || 'info' }}
+        shell: bash
+        run: |
+          docker run --rm \
+            --memory=6g \
+            --memory-swap=6g \
+            -e RENOVATE_PLATFORM=gitea \
+            -e RENOVATE_ENDPOINT=https://gitlab.epicnabbo.nl/ \
+            -e RENOVATE_TOKEN \
+            -e RENOVATE_REPOSITORIES='["remco/EpicNext-Cms"]' \
+            -e RENOVATE_AUTODISCOVER=false \
+            -e RENOVATE_BINARY_SOURCE=install \
+            -e LOG_LEVEL \
+            "renovate/renovate:${RENOVATE_VERSION}"