Fix hardcoded user-facing strings — localize email fallbacks, API errors, AI parse messages

- Frontend: update extractApiError to check body.code first via i18n 'error.<code>' keys;
  add en/ro translations for cv_file_missing, captcha_verification_failed, request_cancelled
- email-data migration: seed 6 fallback template keys (match N/A, subject label, unknown IP,
  job search results empty states for keywords/providers/location)
- EmailApiEmailSender: replace "N/A", "Job", "Unknown" literals with template lookups
- CvSearchEmailSender: replace "none detected", "none", "-" literals with template lookups
- cv-matcher-data migration: seed parse-error.summary and parse-error.recommendation in AiPrompts
- CvMatcherService: look up localized parse-error messages from AiPrompts before calling ParseResult

Closes #53

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

Apis/api/Services/EmailApiEmailSender.cs

@@ -138,7 +138,7 @@ public sealed class EmailApiEmailSender : IEmailSender
               </tr>
               <tr style="background:#f8f9fa">
                 <td style="font-weight:600;border:1px solid #dee2e6;color:#495057">IP Address</td>
-                <td style="border:1px solid #dee2e6">{userIp ?? "Unknown"}</td>
+                <td style="border:1px solid #dee2e6">{userIp ?? _emailTemplates.Get("email.notification.unknown-ip", "en")}</td>
               </tr>
             </table>
             """;
@@ -215,8 +215,8 @@ public sealed class EmailApiEmailSender : IEmailSender
         // email.match.body is now stored as HTML in the database
         var body = _emailTemplates.Render("email.match.body", language,
             ("cvDocumentId", cvDocumentId),
-            ("jobLabel", jobLabel ?? "N/A"),
-            ("jobUrl", result.JobUrl ?? "N/A"),
+            ("jobLabel", jobLabel ?? _emailTemplates.Get("email.match.fallback-na", language)),
+            ("jobUrl", result.JobUrl ?? _emailTemplates.Get("email.match.fallback-na", language)),
             ("score", result.Score.ToString()),
             ("summary", WebUtility.HtmlEncode(result.Summary ?? string.Empty)),
             ("strengths", strengths),
@@ -238,7 +238,7 @@ public sealed class EmailApiEmailSender : IEmailSender
     public string BuildMatchEmailSubject(int score, string? jobLabel, string language) =>
         _emailTemplates.Render("email.match.subject", language,
             ("score", score.ToString()),
-            ("jobLabel", jobLabel ?? "Job"));
+            ("jobLabel", jobLabel ?? _emailTemplates.Get("email.match.subject-fallback-label", language)));
 
     public string GetManualJobLabel(string language) =>
         _emailTemplates.Get("email.match.manual-job-label", language);