CI: re-add missing COOLIFY_* repo secrets — preview deploys marked non-blocking

[SabaTech-dev]

Context

Since at least 2026-08-22, every PR in this repo fails Deploy Backend Preview and Deploy Frontend Preview at the "Log in to Coolify Registry" step because the `COOLIFY_` repo secrets are absent from GitHub (verified via `gh secret list` 2026-08-23: only JOKERSERVER_PAT, LLAMA_API_KEY, RAILWAY_ exist).

Secrets to re-add (used by .github/workflows/pr-deploy-coolify.yml)

• `COOLIFY_REGISTRY_URL`
• `COOLIFY_REGISTRY_USERNAME`
• `COOLIFY_REGISTRY_PASSWORD`
• `COOLIFY_API_URL`
• `COOLIFY_API_TOKEN`
• `COOLIFY_BACKEND_APP_ID`
• `COOLIFY_FRONTEND_APP_ID`
• `COOLIFY_FRONTEND_PREVIEW_API_URL`

Requires repo admin/owner (Joker/Alfred) — values live in the Coolify instance settings / password manager.

Interim mitigation (PR fixing repo-wide CI rot)

The preview-deploy jobs are marked `continue-on-error: true` so the missing secrets no longer rot the CI signal for every PR. Once the secrets are re-added:

1. Revert the `continue-on-error` lines in `pr-deploy-coolify.yml` (search for this issue number).
2. Re-run the deploy job on any open PR to verify login + preview deploy.

Related: repo-wide CI rot fixed in the same effort (semgrep SARIF upload, PR-validation heredoc, black repo-wide) — see the linked PR.