Add language assistant settings and related features: Introduce new routes and controller methods for managing language assistant settings, including retrieval and saving of LLM configurations. Update navigation structure to include language assistant options. Enhance vocab course model to support additional learning attributes such as learning goals and core patterns. Update SQL scripts to reflect new database schema changes for vocab courses. Improve localization for language assistant settings in German and English.

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

@@ -150,6 +150,27 @@
             "changeaction": "Change User Data",
             "oldpassword": "Old Password (required)"
         },
+        "languageAssistant": {
+            "eyebrow": "Settings",
+            "title": "Language assistant & AI",
+            "intro": "Store your own API access (e.g. OpenAI) for language-course features. The key is encrypted on the server. You need an account with the provider.",
+            "linkSignup": "Create an OpenAI account (new tab)",
+            "linkApiKeys": "Manage OpenAI API keys (new tab)",
+            "enabled": "Allow use for language features",
+            "baseUrl": "API base URL (optional)",
+            "baseUrlPlaceholder": "Empty = default (OpenAI). For Ollama e.g. http://127.0.0.1:11434/v1",
+            "model": "Model name",
+            "apiKey": "API key",
+            "apiKeyHint": "Leave empty to keep the stored key.",
+            "apiKeyPlaceholderNew": "Paste new key",
+            "apiKeyPlaceholderHasKey": "Saved key ends with …{last4} — leave empty to keep",
+            "apiKeyPlaceholderClear": "Storage will be cleared when you save with “Remove key” below",
+            "clearKey": "Remove stored API key",
+            "save": "Save",
+            "saved": "Settings saved.",
+            "saveError": "Could not save.",
+            "confirmClear": "Really delete the API key?"
+        },
         "interests": {
             "title": "Interests",
             "new": "New Interest",