refactor(dashboard): collapse usage section into a single row

Merge the two "by Model" pies (Token Usage + API Requests) into one
dual-pie card with a shared right-side vertical legend and per-donut
center totals, drop the standalone API-Key Top 10 chart, and put the
combined chart side-by-side with the User Top 10 ranking in one row
with the same 16/8 column ratio used by the System Load section above.

* New component usage-charts/usage-by-model.tsx owns both metric queries
  (group_by=['date','route']), aggregates a shared route→color map so
  the legend toggles both donuts together, and renders two pies at
  centers ('20%','50%') and ('60%','50%') with radius ['50%','70%'].
* new-usage.tsx no longer mounts ApiRequestsByModel / TokenUsageByModel
  / TopTokenUsageByApiKey; layout collapses to two columns sized
  (lg=24 xl=16) and (lg=24 xl=8).
* Delete unused token-usage-by-model.tsx, api-requests-by-model.tsx,
  top-token-usage-by-api-key.tsx, and the use-top-token-usage-by-api-key
  hook.
* Strip the now-unreferenced dashboard.tokenUsageByModel /
  apiRequestsByModel / topTokenUsageByApiKey locale keys across 5
  locales, add the new dashboard.usageByModel title; locale parity
  check passes.

src/locales/ru-RU/dashboard.ts

@@ -13,10 +13,8 @@ export default {
   'dashboard.tokens': 'Использование токенов',
   'dashboard.topusers': 'Топ пользователей',
   'dashboard.activeDeployments': 'Active Deployments',
-  'dashboard.tokenUsageByModel': 'Использование токенов по моделям',
-  'dashboard.apiRequestsByModel': 'API-запросы по моделям',
+  'dashboard.usageByModel': 'Использование по моделям',
   'dashboard.topTokenUsageByUser': 'Топ-10 пользователей по токенам',
-  'dashboard.topTokenUsageByApiKey': 'Топ-10 API-ключей по токенам',
   'dashboard.allocatevram': 'Выделено VRAM / ОЗУ',
   'dashboard.usage.selectuser': 'Выбрать пользователей',
   'dashboard.usage.selectmodel': 'Выбрать модели',