Make discover count machine-readable for CI parsing

The workflow's grep-on-free-text approach was fragile: local run correctly
extracted 162, but in the CI run the 'Open issue' step was skipped, meaning
new_count ended up as 0 after parsing. Likely causes: stdout buffering,
color codes, or shell differences between local and the Gitea runner's
shell.

Fix: tools/refresh_sku_catalog.py --discover now emits a deterministic
last-line marker `DISCOVER_MISSING_COUNT=<n>`. The workflow parses that
with sed (anchored, unambiguous) instead of the human-facing summary
line. Also added a diagnostic echo so the parsed value shows up in CI
logs for future debugging.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/sku-catalog-refresh.yaml

@@ -61,8 +61,9 @@ jobs:
         run: |
           python3 tools/refresh_sku_catalog.py --discover -v 2>&1 \
             | tee /tmp/discover.log
-          NEW_COUNT=$(grep -oE '^[0-9]+ SKUs present in API' /tmp/discover.log \
-            | head -1 | awk '{print $1}' || echo "0")
+          NEW_COUNT=$(sed -n 's/^DISCOVER_MISSING_COUNT=\([0-9]\+\)$/\1/p' \
+            /tmp/discover.log | tail -1)
+          echo "Parsed new_count='${NEW_COUNT}'"
           echo "new_count=${NEW_COUNT:-0}" >> $GITHUB_OUTPUT
 
       - name: Upload logs as artifact