feat: run Renovate via Dagger on daily schedule (#257, #216)

Adds a Renovate() Dagger function using the forgejo platform and a
.forgejo/workflows/renovate.yml workflow triggered at 06:00 UTC daily.
Uses RENOVATE_FORGEJO_TOKEN secret; no dedicated Renovate service account needed.

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

.forgejo/workflows/renovate.yml

@@ -0,0 +1,33 @@
+name: Renovate
+
+on:
+  schedule:
+    - cron: '0 6 * * *'
+  workflow_dispatch:
+
+jobs:
+  renovate:
+    name: Renovate
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Dagger Remote Engine (via stunnel)
+        env:
+          DAGGER_STUNNEL_URL: ${{ secrets.DAGGER_STUNNEL_URL }}
+          DAGGER_CA_CERT: ${{ secrets.DAGGER_CA_CERT }}
+          DAGGER_CLIENT_CERT: ${{ secrets.DAGGER_CLIENT_CERT }}
+          DAGGER_CLIENT_KEY: ${{ secrets.DAGGER_CLIENT_KEY }}
+        run: scripts/setup_dagger_remote.sh
+
+      - name: Run Renovate
+        env:
+          DAGGER_NO_NAG: "1"
+          RENOVATE_FORGEJO_TOKEN: ${{ secrets.RENOVATE_FORGEJO_TOKEN }}
+        run: task renovate
+
+      - name: Cleanup TLS credentials
+        if: always()
+        run: rm -rf /tmp/dagger-tls /tmp/stunnel-dagger.conf /tmp/stunnel.pid