DEV-1168: Add advisory PR title check for Linear ticket IDs

[saicheems]

We want all PRs across the org to be associated with a Linear ticket. This adds a non-enforced GitHub Action to the org-wide .github repo that checks PR titles for a Linear ticket ID prefix. It runs on every PR in every gradienthealth repo — shows pass/fail but doesn't block merging.

• Add a workflow that validates PR titles start with a ticket ID pattern (e.g., ATL-123, dev-456, PROC 789)
• Case-insensitive, supports both hyphen and space separators to match existing team conventions

Once adoption is consistent, this can be promoted to a required check to block merging.

[linear]

DEV-1168 Enforce Linear ticket IDs on all GitHub PRs

All PRs across the org should be associated with a Linear ticket via the PR title (e.g. ENG-123 Add foo).

Phase 1: Add a non-enforced GitHub Action in gradienthealth/.github that checks PR titles for a Linear ticket ID pattern. Shows pass/fail as an advisory status check — doesn't block merging.

Phase 2: Promote to a required workflow or org ruleset so PRs without a ticket ID can't merge.