feat(localization): Implement Swedish localization and error messages

- Added localization support for Swedish and English languages.
- Integrated localized strings for user messages in the API error mapper.
- Updated UI components to use localized strings for labels and messages.
- Ensured all error messages are context-aware and utilize the localization framework.
- Created regression test to prevent common ASCII fallbacks in Swedish UI text.

flutter/lib/l10n/app_en.arb

@@ -0,0 +1,16 @@
+{
+  "@@locale": "en",
+  "appTitle": "Recipe App",
+  "retryAction": "Retry",
+  "loginTitle": "Sign in",
+  "usernameLabel": "Username",
+  "usernameRequired": "Enter your username.",
+  "passwordLabel": "Password",
+  "passwordRequired": "Enter your password.",
+  "loginAction": "Sign in",
+  "sessionExpiredError": "Your session has expired. Sign in again.",
+  "forbiddenError": "You do not have permission to use this feature.",
+  "serverError": "A server error occurred. Try again in a moment.",
+  "networkError": "Network error. Check your connection and try again.",
+  "unexpectedError": "An unexpected error occurred."
+}

flutter/lib/l10n/app_sv.arb

@@ -0,0 +1,16 @@
+{
+  "@@locale": "sv",
+  "appTitle": "Recipe App",
+  "retryAction": "Försök igen",
+  "loginTitle": "Logga in",
+  "usernameLabel": "Användarnamn",
+  "usernameRequired": "Ange ditt användarnamn.",
+  "passwordLabel": "Lösenord",
+  "passwordRequired": "Ange ditt lösenord.",
+  "loginAction": "Logga in",
+  "sessionExpiredError": "Din session har gått ut. Logga in igen.",
+  "forbiddenError": "Du saknar behörighet för denna funktion.",
+  "serverError": "Serverfel uppstod. Försök igen om en stund.",
+  "networkError": "Nätverksfel. Kontrollera anslutningen och försök igen.",
+  "unexpectedError": "Ett oväntat fel uppstod."
+}