feat(models): add group-by-model option to collapse multiple versions into one card

Adds a 'Group by Model' toggle in Layout Settings. When enabled, only the
latest version (highest civitai.id) of each Civitai model is shown as a
single card — older versions sharing the same modelId are hidden.

Backend dedup runs in BaseModelService.get_paginated_data() before
filtering/pagination, ensuring correct paginated results. The setting
is persisted via the existing settings pipeline and passed as a query
parameter to the listing endpoint.

Includes:
- Backend: dedup logic, route param parsing, settings default
- Frontend: API param, SettingsManager wiring, toggle UI
- i18n: translations for all 10 locales
- Tests: unit test covering dedup on/off and standalone items

static/js/state/index.js

@@ -54,6 +54,7 @@ const DEFAULT_SETTINGS_BASE = Object.freeze({
     backup_retention_count: 5,
     strip_lora_on_copy: false,
     use_new_license_icons: true,
+    group_by_model: false,
 });
 
 export function createDefaultSettings() {