The TCP monitor creation form showed a placeholder that instructed users to enter a URL with the tcp:// scheme prefix (e.g., tcp://192.168.1.1:8080). Following this guidance caused a silent HTTP 500 error because Go's net.SplitHostPort rejects any input containing a scheme prefix, expecting bare host:port format only.
- Corrected the urlPlaceholder translation key to remove the tcp:// prefix
- Added per-type dynamic placeholder (urlPlaceholderHttp / urlPlaceholderTcp) so the URL input shows the correct example format as soon as the user selects a monitor type
- Added per-type helper text below the URL input explaining the required format, updated in real time when the type selector changes
- Added client-side validation: typing a scheme prefix (://) in TCP mode shows an inline error and blocks form submission before the request reaches the backend
- Reordered the Create Monitor form so the type selector appears before the URL input, giving users the correct format context before they type
- Type selector onChange now clears any stale urlError to prevent incorrect error messages persisting after switching from TCP back to HTTP
- Added 5 new i18n keys across all 5 supported locales (en, de, fr, es, zh)
- Added 10 RTL unit tests covering all new validation paths including the type-change error-clear scenario
- Added 9 Playwright E2E tests covering placeholder variants, helper text, inline error lifecycle, submission blocking, and successful TCP creation
Closes #issue-5 (TCP monitor UI cannot add monitor when following placeholder)
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