Skip preview branch creation via PR title or label

Feature Request Allow skipping Supabase preview branch creation when a PR title contains a specific pattern (e.g., [skip preview], [skip supabase]) or has a specific label (e.g., skip-supabase). Use Case Infrastructure-only PRs (CI/CD workflow changes, documentation, frontend-only changes) that don't need a database branch but still go through the PR workflow. Currently, every PR triggers a Supabase preview branch creation, which: • Consumes branch quota unnecessarily • Adds deployment time for PRs that don't touch the database • Creates clutter in the branches list Current Workarounds The "Supabase changes only" option helps, but doesn't cover cases where: • You want to skip even when supabase/ files change (e.g., config-only updates, comments in migrations) • You have a mixed PR but want to test against staging/production database instead Proposed Solution Similar to how CI systems support [skip ci] in commit messages, a…