chore(ci): run the coverage report only when a report exists

`always()` ran the coverage action even when `npm ci` or `npm run lint`
had already failed. No coverage file exists at that point, so the action
failed with ENOENT and became the last red step in the job. That hid the
real cause, which is what happened on #126 and #130.

`!cancelled()` keeps the useful half of `always()`: the report still runs
when the test step fails, which is the point of `reportOnFailure: true`
in vitest.config.ts. It drops the half nobody wants, which is running the
step after you cancel the job.

The `hashFiles` guard skips the step when there is no coverage file to
publish.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttm65yYvBRc7DBwguJW1XE

Author: damonbauer

.github/workflows/pr.yml

@@ -26,4 +26,4 @@ jobs:
       - run: npm run test:coverage
 
       - uses: davelosert/vitest-coverage-report-action@v2
-        if: always()
+        if: ${{ !cancelled() && hashFiles('coverage/coverage-summary.json') != '' }}