chore(ci): push-triggered staging diagnostic workflow (temporary)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitea/workflows/diag-staging.yml

@@ -0,0 +1,26 @@
+# TEMPORARY diagnostic workflow — delete after the rankings year= bug is closed.
+name: Staging Rankings Diagnostic
+
+on:
+  push:
+    branches:
+      - diag/staging-rankings-year
+
+jobs:
+  staging-api-diagnostic:
+    name: Staging rankings year diagnostic
+    runs-on: ubuntu-latest
+    steps:
+      - name: Probe staging rankings year handling
+        env:
+          BASE: ${{ secrets.STAGING_BASE_URL }}
+        run: |
+          echo "== /api/filters years =="
+          curl -s --max-time 15 "$BASE/api/filters" -o /tmp/f.json -w "status %{http_code}\n"
+          python3 -c "import json; print(json.load(open('/tmp/f.json')).get('years'))" || head -c 300 /tmp/f.json
+          echo "== /api/rankings probes (metric=rwm_expected_pct, limit=3) =="
+          for Q in "" "&year=202425" "&year=201819" "&year=2024"; do
+            CODE=$(curl -s --max-time 15 -o /tmp/r.json -w "%{http_code}" "$BASE/api/rankings?metric=rwm_expected_pct&limit=3$Q")
+            echo "query [$Q] -> status $CODE"
+            python3 -c "import json; d=json.load(open('/tmp/r.json')); print('  year:', d.get('year'), 'total:', d.get('total'), 'rows:', len(d.get('rankings', [])))" || head -c 300 /tmp/r.json
+          done