PROC-1513: accept Conventional Commit titles with Linear ID in scope (#6)

## Summary
Widen the PR title check so titles like `feat(ENG-123): add feature` are
accepted in addition to the existing `ENG-123: ...` and `NO-ISSUE:`
formats.

## Why
Adopting [release-please](https://github.com/googleapis/release-please)
in `cloud_optimized_dicom` (see [PR
#97](gradienthealth/cloud_optimized_dicom#97))
requires PR titles to start with a Conventional Commit type prefix
(`feat:`, `fix:`, `chore:`, etc.) so the bot can decide the next
version. The existing org-level check requires the Linear ID at the very
start, which conflicts. Putting the Linear ID inside the
conventional-commit scope (`feat(ENG-123): ...`) satisfies both worlds,
but the current regex doesn't recognize it.

## Change
Two new branches added to the existing if/elif chain:
- Conventional Commit with Linear ID in scope: `feat(ENG-123): add
feature`
- Conventional Commit with `NO-ISSUE` opt-out: `chore: NO-ISSUE refactor
internals`

Existing formats continue to pass — pure superset, zero behavior change
for repos not adopting Conventional Commits.

## Test plan
- [ ] Title `ENG-123: existing format` → passes (unchanged)
- [ ] Title `feat(ENG-123): new format` → passes (new)
- [ ] Title `NO-ISSUE: opt-out` → passes (unchanged)
- [ ] Title `chore: NO-ISSUE thing` → passes (new)
- [ ] Title `random title with no marker` → fails

Author: CalNightingale

.github/workflows/pr-title-check.yml

@@ -21,9 +21,13 @@ jobs:
             echo "Bot PR — skipping check."
           elif echo "$PR_TITLE" | grep -qPi '^[A-Z]+[-\s]\d+\b'; then
             echo "PR title starts with a Linear issue ID."
+          elif echo "$PR_TITLE" | grep -qP '^[a-z]+(\([^)]*[A-Z]+[-\s]\d+[^)]*\))!?:'; then
+            echo "PR title is a Conventional Commit with a Linear issue ID in scope."
           elif echo "$PR_TITLE" | grep -qPi '^NO-ISSUE\b'; then
             echo "::notice::PR explicitly opted out of issue association."
+          elif echo "$PR_TITLE" | grep -qPi '^[a-z]+(\([^)]*\))?!?:\s*NO-ISSUE\b'; then
+            echo "::notice::PR explicitly opted out of issue association (conventional commit style)."
           else
-            echo "::error::PR title must start with a Linear issue ID (e.g., \"ENG-123: Add feature\") or \"NO-ISSUE:\" to opt out."
+            echo "::error::PR title must start with a Linear issue ID (e.g., \"ENG-123: Add feature\"), include one in a conventional-commit scope (e.g., \"feat(ENG-123): add feature\"), or use \"NO-ISSUE\" to opt out."
             exit 1
           fi