Implement password prompt UI and logic in MultiChatDialog: Add a password entry panel with validation and error handling for room access. Update i18n files for localized password prompts in English, German, and Spanish.

frontend/src/i18n/locales/de/chat.json

@@ -116,6 +116,10 @@
                 "types": {}
             },
             "password": {
+                "title": "Passwort erforderlich",
+                "inputLabel": "Passwort eingeben",
+                "submit": "Beitreten",
+                "cancel": "Abbrechen",
                 "requiredPrompt": "Der Raum \"{room}\" ist passwortgeschützt. Bitte Passwort eingeben:",
                 "invalidPrompt": "Falsches Passwort für \"{room}\". Bitte erneut eingeben:",
                 "cancelled": "Beitritt zu \"{room}\" abgebrochen.",

frontend/src/i18n/locales/en/chat.json

@@ -116,6 +116,10 @@
                 "types": {}
             },
             "password": {
+                "title": "Password required",
+                "inputLabel": "Enter password",
+                "submit": "Join room",
+                "cancel": "Cancel",
                 "requiredPrompt": "Room \"{room}\" is password-protected. Please enter password:",
                 "invalidPrompt": "Wrong password for \"{room}\". Please try again:",
                 "cancelled": "Join to \"{room}\" was cancelled.",

frontend/src/i18n/locales/es/chat.json

@@ -115,6 +115,10 @@
                 "types": {}
             },
             "password": {
+                "title": "Contraseña requerida",
+                "inputLabel": "Introduce la contraseña",
+                "submit": "Entrar en sala",
+                "cancel": "Cancelar",
                 "requiredPrompt": "La sala \"{room}\" está protegida por contraseña. Introduce la contraseña:",
                 "invalidPrompt": "Contraseña incorrecta para \"{room}\". Inténtalo de nuevo:",
                 "cancelled": "Se canceló el acceso a \"{room}\".",