feat(ci): wire up gpt-4o-mini for issue classification

- Replace stub callGitHubModel() with real GitHub Models API call
  using gpt-4o-mini with structured JSON output
- Build detailed user messages from issue body, comments, and timeline
- Add per-issue decision logging to classify step
- Upload candidates.json and decisions.json as workflow artifacts

.github/workflows/issue-resolution-triage.yml

@@ -53,4 +53,12 @@ jobs:
 
       - run: node scripts/fetch-candidates.mjs
       - run: node scripts/classify-candidates.mjs
-      - run: node scripts/apply-decisions.mjs
+      - run: node scripts/apply-decisions.mjs
+
+      - uses: actions/upload-artifact@v4
+        if: always()
+        with:
+          name: triage-results
+          path: |
+            .github/issue-resolution/candidates.json
+            .github/issue-resolution/decisions.json