feat(frontend): opt-in Other Models toggles, hidden nav and announcement

- The Other nav entry is hidden while the feature is off
  (nav-item--hidden, toggled client-side after enabling) and now uses the
  fa-shapes icon.
- Shared utils/otherModels.js helpers (enable through the settings API,
  open the settings Library section) are reused by the disabled page, the
  announcement banner and the download modal.
- BannerService registers a one-time dismissible "other-models-announcement"
  banner while the feature is off; SettingsManager drops the banner and
  updates the nav when the master switch flips.
- A disabled download routing answer now surfaces a showActionToast with an
  "Enable Other Models" action.
- Settings UI: master toggle + five sub_type checkboxes whose default-root
  selects are disabled when unchecked; i18n keys added to en.json and synced
  (other locales keep TODO placeholders).

static/js/utils/otherModels.js

@@ -0,0 +1,52 @@
+/**
+ * Shared helpers for the opt-in Other Models feature.
+ *
+ * Used by the disabled page, the announcement banner and the download modal so
+ * that enabling the feature always goes through the same settings API call and
+ * lands on the same settings section.
+ */
+
+/**
+ * Turn on Other Models management and reload so the server-rendered nav and
+ * the scanner state pick up the change.
+ */
+export async function enableOtherModels() {
+    const response = await fetch('/api/lm/settings', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ enable_other_models: true }),
+    });
+    const data = await response.json().catch(() => ({}));
+    if (!response.ok || data.success === false) {
+        throw new Error(data.error || `HTTP ${response.status}`);
+    }
+    window.location.reload();
+}
+
+/**
+ * Open the settings modal on the Library section and scroll the Other Models
+ * toggle into view. Mirrors DoctorManager's open-settings-syntax-format flow.
+ */
+export function openOtherModelsSettings() {
+    const modalManager = window.modalManager;
+    if (modalManager && typeof modalManager.showModal === 'function') {
+        modalManager.showModal('settingsModal');
+    }
+
+    window.setTimeout(() => {
+        document.querySelectorAll('.settings-section').forEach((section) => {
+            section.classList.remove('active');
+        });
+        document.getElementById('section-library')?.classList.add('active');
+
+        document.querySelectorAll('.settings-nav-item').forEach((item) => {
+            item.classList.remove('active');
+        });
+        document.querySelector('.settings-nav-item[data-section="library"]')?.classList.add('active');
+
+        document.getElementById('enableOtherModels')?.scrollIntoView({
+            behavior: 'smooth',
+            block: 'center',
+        });
+    }, 100);
+}