smtp: typed probe errors with per-field UI highlighting on save

TODO.md

@@ -65,9 +65,20 @@
 
 ## SMTP credential validation
 
-- [x] Add `SmtpRelay::test()` — connect + EHLO + STARTTLS + AUTH + QUIT, no message sent
-- [x] Add `SmtpRelay::smtpProbe()` — private low-level probe (mirrors smtpSend without envelope/data)
-- [x] Wire into `actions/settings.php` SMTP branch: probe immediately after save, flash success or error with detail
+- [x] Add `SmtpProbeException` with `field` property for structured error classification
+- [x] Add `SmtpRelay::test()` — returns `{ok, error, field}` with field = input id to highlight
+- [x] `smtpProbe()` throws typed exceptions per failure point:
+  - connect fail → name resolution error → `smtp_host`
+  - connect fail → port refused → `smtp_port`
+  - connect fail → timeout → `smtp_host`
+  - bad greeting / timeout after connect → `smtp_host` / `smtp_port`
+  - STARTTLS not supported / TLS negotiation fail → `smtp_encryption`
+  - AUTH rejected, code 535 → `smtp_password`; other auth failures → `smtp_username`
+- [x] `actions/settings.php`: store `$_SESSION['_flash_smtp_field']` on probe failure
+- [x] `parametres.php` controller: consume + clear `_flash_smtp_field` into `$smtpErrorField`
+- [x] Template: `aria-invalid`, `aria-describedby`, inline `<small class="param-field-error">` per field
+- [x] JS: scroll + focus the offending field on page load
+- [x] CSS: red `border-bottom` on `[aria-invalid]`, `.param-field-error` error text style
 
 ## Répertoire layout