chore(admin): add contract audit baseline and incomplete build notice

Introduce tools/audit-admin-contracts.php to fail on missing schemaPage
sections, missing REST $this callbacks, and incomplete admin build chunks.
Document menu/schema deploy rules and surface a wp-admin error when
assets/admin/build is missing modules instead of failing silently.

.gitignore

@@ -21,4 +21,8 @@ restore-helper-monoliths.php
 # OS / editor noise
 .DS_Store
 Thumbs.db
-*.log
+*.log
+
+
+# Generated contract audit artifact
+tools/admin-contract-report.json