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>

web/wwwroot/js/utils/form-helpers.js

@@ -52,6 +52,7 @@ function isValidEmail(value) {
  *
  * Rules:
  * - 429 (rate limit) → return rateLimitKey translation
+ * - 4xx with known error code → look up 'error.<code>' in i18n dictionary first
  * - 4xx with error body → return server's error message (intentional feedback)
  * - 5xx or no body → return fallbackKey translation
  *
@@ -65,8 +66,17 @@ function extractApiError(body, status, fallbackKey, rateLimitKey) {
 	if (status === 429) {
 		return window.MyAi.t(rateLimitKey || 'form.rateLimited');
 	}
-	var msg = body && (body.error || body.Error || body.title);
-	return (status >= 400 && status < 500 && msg) ? msg : window.MyAi.t(fallbackKey);
+	if (status >= 400 && status < 500) {
+		// Prefer i18n translation keyed on the machine-readable error code
+		if (body && body.code) {
+			var codeKey = 'error.' + body.code;
+			var translated = window.MyAi.t(codeKey);
+			if (translated !== codeKey) return translated;
+		}
+		var msg = body && (body.error || body.Error || body.title);
+		if (msg) return msg;
+	}
+	return window.MyAi.t(fallbackKey);
 }
 
 // Expose helpers on window.MyAi for use by other scripts