feat(smtp): add a precious SMTP test for admin only

static/locales/en.json

@@ -649,7 +649,23 @@
         "migration_verify_passed": "Verification passed",
         "migration_verify_failed": "Verification failed",
         "migration_failed_blobs": "failed blobs",
-        "testing": "Testing…"
+        "testing": "Testing…",
+        "tab_smtp": "SMTP",
+        "smtp_title": "Outbound Email (SMTP)",
+        "smtp_intro": "SMTP is configured exclusively via environment variables (OXICLOUD_SMTP_*). The values below are read from the running server — to change them, edit the environment and restart OxiCloud.",
+        "smtp_enabled_label": "Status",
+        "smtp_enabled": "Enabled",
+        "smtp_disabled": "Disabled (host unset)",
+        "smtp_test_title": "Send a test email",
+        "smtp_test_intro": "Sends a hardcoded diagnostic message to the recipient below and reports the SMTP server's response so you can correlate it with your relay logs.",
+        "smtp_test_to": "Recipient address",
+        "smtp_send_test": "Send test email",
+        "smtp_sending": "Sending…",
+        "smtp_sent": "Test email sent.",
+        "smtp_send_failed": "Send failed.",
+        "smtp_server_code": "Server replied",
+        "smtp_test_missing_to": "Enter a recipient address.",
+        "smtp_not_configured": "SMTP is not configured on this server."
     },
     "profile": {
         "page_title": "Profile",