Add Forgejo Actions workflows: CI, image build+push, ops cron (#236)

Three workflows for the self-hosted Forgejo instance (Track A chunk 7 of the
infra-design implementation handoff), mirroring/extending the existing
.github/workflows without touching them - GitHub stays the primary repo and
its own build.yml/ci-cd.yml keep gating auto-merge.

ci.yml mirrors build.yml's build gate (deps, backend tests, frontend JS
syntax check, boot + page/API health check) on a Forgejo runner.

build-push.yml builds the app image and pushes it to Forgejo's built-in
registry, tagged by git SHA (every push) and semver (version tags) - the
registry half of the hop-1 cutover's build-once/deploy-everywhere model.
Runs alongside the existing deploy.yml/deploy.sh (git-checkout-and-build-in-
place) without touching it, per the cutover runbook's Stage C.

ops-cron.yml runs a daily pg_dump backup and an IndexNow --if-changed ping,
both via SSH into the prod host (the same SSH secrets deploy.yml already
uses) using the app's already-running compose stack - no new network
exposure, no separate dependency install. These are ops/infra concerns
(scheduled via Forgejo Actions cron), distinct from the app-domain jobs the
worker's own APScheduler runs.

All three need a runner registered with the `thermograph` label and the
registry's public/mesh exposure resolved (Track B).

Verified: raw YAML syntax valid; actionlint clean except the pre-existing,
already-present-on-.github/workflows "unknown custom runner label" warning
(not something these files introduce - the existing thermograph-lan label
triggers the identical warning). One real finding fixed pre-commit: an
unused shellcheck-flagged loop variable in the boot-check retry loop.

.forgejo/workflows/ops-cron.yml

@@ -0,0 +1,64 @@
+name: Ops cron (backup + IndexNow)
+
+# Scheduled operational jobs that don't belong in the app's own worker-tier
+# scheduler (notifications/scheduler.py, Track A chunk 5) because they're
+# infra/ops concerns rather than app-domain background work -- see the job
+# classification table in
+# docs/architecture/repo-topology-and-infrastructure.md §7.
+#
+# Both jobs SSH into the prod host and run inside the already-running compose
+# stack (docker compose exec), the same way deploy.sh already runs its own
+# post-deploy IndexNow ping -- no new network exposure, no separate dependency
+# install. Needs a runner registered with the `thermograph` label (Track B step
+# 5) and the same SSH secrets deploy.yml uses (SSH_HOST/SSH_USER/SSH_KEY/
+# SSH_PORT) to reach the prod host.
+
+on:
+  schedule:
+    # 03:00 UTC daily -- a low-traffic window for both jobs.
+    - cron: '0 3 * * *'
+  workflow_dispatch: {}
+
+jobs:
+  backup:
+    name: pg_dump backup
+    runs-on: [self-hosted, thermograph]
+    steps:
+      - name: Dump the prod database over SSH
+        uses: appleboy/ssh-action@v1.2.0
+        with:
+          host: ${{ secrets.SSH_HOST }}
+          username: ${{ secrets.SSH_USER }}
+          key: ${{ secrets.SSH_KEY }}
+          port: ${{ secrets.SSH_PORT }}
+          script: |
+            set -euo pipefail
+            cd /opt/thermograph
+            backup_dir="$HOME/thermograph-backups"
+            mkdir -p "$backup_dir"
+            stamp="$(date -u +%Y%m%dT%H%M%SZ)"
+            out="$backup_dir/thermograph-$stamp.dump"
+            docker compose exec -T db pg_dump -U thermograph -d thermograph \
+              --format=custom > "$out"
+            echo "wrote $out ($(du -h "$out" | cut -f1))"
+            # The dumps are the disaster-recovery copy, not a versioned
+            # archive -- keep the last 14 days and let the rest age out.
+            find "$backup_dir" -name 'thermograph-*.dump' -mtime +14 -delete
+
+  indexnow:
+    name: IndexNow ping
+    runs-on: [self-hosted, thermograph]
+    steps:
+      - name: Ping IndexNow if the URL set changed
+        uses: appleboy/ssh-action@v1.2.0
+        with:
+          host: ${{ secrets.SSH_HOST }}
+          username: ${{ secrets.SSH_USER }}
+          key: ${{ secrets.SSH_KEY }}
+          port: ${{ secrets.SSH_PORT }}
+          script: |
+            set -euo pipefail
+            cd /opt/thermograph
+            set -a; . /etc/thermograph.env 2>/dev/null || true; set +a
+            docker compose exec -T app python indexnow.py --if-changed \
+              "${THERMOGRAPH_BASE_URL:-https://thermograph.org}"