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

locales/zh-TW.json

@@ -430,6 +430,8 @@
             "help": "啟用後，如果下載歷史服務記錄顯示該版本已下載，LoRA Manager 將跳過下載該模型版本。適用於所有下載流程。"
         },
         "layoutSettings": {
+            "groupByModel": "按模型分組",
+            "groupByModelHelp": "啟用後，每個 Civitai 模型僅顯示最新版本的單張卡片，舊版本將被隱藏。",
             "displayDensity": "顯示密度",
             "displayDensityOptions": {
                 "default": "預設",