Post visual diff images as PR comment on failure

When visual tests fail on a PR, upload each diff PNG to GitHub's CDN
via the issue assets endpoint and post a comment with the images
embedded inline. Also fixes the artifact upload path to point at
.vitest-attachments/ where the actual/diff files live.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -138,14 +138,48 @@ jobs:
         run: pnpm exec playwright install-deps chromium
 
       - name: Run visual regression tests
+        id: visual-tests
         run: pnpm --filter @trails-cool/planner test:visual
 
+      - name: Post diff comment on PR
+        if: failure() && steps.visual-tests.outcome == 'failure' && github.event_name == 'pull_request'
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          diffs=$(find apps/planner/.vitest-attachments -name "*-diff-*.png" 2>/dev/null | sort)
+          if [ -z "$diffs" ]; then exit 0; fi
+
+          body="## Visual regression failures"$'\n\n'
+          body+="| Test | Diff (reference → actual) |"$'\n'
+          body+="|------|--------------------------|"$'\n'
+
+          for diff in $diffs; do
+            # Upload image to GitHub's CDN via the issue assets endpoint
+            response=$(curl -sf -X POST \
+              -H "Authorization: Bearer $GH_TOKEN" \
+              -H "Content-Type: image/png" \
+              -H "Accept: application/json" \
+              --data-binary @"$diff" \
+              "https://uploads.github.com/repos/${{ github.repository }}/issues/${{ github.event.pull_request.number }}/assets?name=$(basename $diff)")
+            url=$(echo "$response" | jq -r '.url // empty')
+            name=$(basename "$diff" | sed 's/-diff-chromium-linux\.png//' | sed 's/-/ /g')
+            if [ -n "$url" ]; then
+              body+="| \`$name\` | ![$name]($url) |"$'\n'
+            else
+              body+="| \`$name\` | *(upload failed)* |"$'\n'
+            fi
+          done
+
+          body+=$'\n'"Run \`pnpm --filter @trails-cool/planner test:visual:update\` to regenerate snapshots if the change is intentional."
+
+          gh pr comment ${{ github.event.pull_request.number }} --body "$body"
+
       - name: Upload screenshots on failure
         if: failure()
         uses: actions/upload-artifact@v7
         with:
           name: visual-snapshots-diff
-          path: apps/planner/app/**/__screenshots__/
+          path: apps/planner/.vitest-attachments/
           retention-days: 7
 
   e2e: