fix: fetch commit subject via Gitea API instead of git log

Notification job had no checkout step so git log always failed,
producing "Commit info unavailable". Now uses the existing
API_GITEA_TOKEN and gitea.sha context to fetch the commit message
from the Gitea API directly.

Also raises default coverage threshold in python-checks to 80%.

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

.gitea/workflows/python-checks.yml

@@ -17,7 +17,7 @@ on:
         default: "coverage run -m pytest"
       coverage_fail_under:
         type: string
-        default: "60"
+        default: "80"
       run_security_scan:
         type: boolean
         default: true