Add git/docs rules to AGENTS.md; add docs reminder to presubmit

scripts/presubmit.py

@@ -53,3 +53,7 @@ def presubmit():
         print(f"\nFailed: {', '.join(failed)}", file=sys.stderr)
         sys.exit(1)
     print("\nAll presubmit checks passed.")
+    print(
+        "\nReminder: if this task changed architecture, layer boundaries, config schema,\n"
+        "directory layout, API endpoints, or the plugin system — update docs/overview.md."
+    )