feat: replace SmtpEmailSender with EmailApiEmailSender in api

- EmailApiEmailSender calls email-api via IEmailApiClient Refit client
- HTML bodies built inline for contact/subscribe/file-download emails
- match and job-search emails use DB templates (rendered in caller)
- SmtpSettings moved from api-models to email-api (kept in Models.Settings namespace)
- MailKit removed from api.csproj
- SmtpEmailSender deleted; IEmailSender interface unchanged

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Apis/email-api/Settings/SmtpSettings.cs

@@ -0,0 +1,10 @@
+namespace Models.Settings;
+
+public sealed class SmtpSettings
+{
+    public string Host { get; set; } = "";
+    public int Port { get; set; } = 587;
+    public string Username { get; set; } = "";
+    public string Password { get; set; } = "";
+    public bool UseStartTls { get; set; } = true;
+}