ci: QA suite (repo+live), Gitea Actions workflow, app config-as-code

- qa/site-qa.sh: repo structure/link checks + full live crawl (routes,
  links, assets, canonical-https)
- .gitea/workflows/qa.yml: repo QA on push, nightly live QA
- app/: config-as-code for the deployed sync job, scheduler entry,
  and Grav system.yaml (reverse-proxy HTTPS detection)
- local pre-push hook runs repo QA

https://projects.knownelement.com/issues/928

app/scheduler/git-sync.job.yaml

@@ -0,0 +1,4 @@
+enabled: true
+run_at: '*/15 * * * *'
+command: /bin/bash /app/data/git-sync-job.sh
+output: logs/git-sync-job.log