feat: Implement token issue detection and enhance license validation middleware; add tests for token issue message detection

backend/tests/unit/core/test_license_middleware.py

@@ -0,0 +1,21 @@
+from core.middleware import _is_token_issue_message
+
+
+def test_is_token_issue_message_detects_expired_token_in_spanish():
+    assert _is_token_issue_message("Token inválido o expirado") is True
+
+
+def test_is_token_issue_message_detects_expired_token_in_english():
+    assert _is_token_issue_message("Invalid or expired token") is True
+
+
+def test_is_token_issue_message_detects_detail_reason_combo():
+    assert _is_token_issue_message(
+        "Access denied",
+        "jwt signature validation failed",
+        "token malformed",
+    ) is True
+
+
+def test_is_token_issue_message_does_not_flag_real_license_error():
+    assert _is_token_issue_message("Sin licencia asignada para este tenant") is False