feat: AI model selector + i18n nav labels (RU/EN) on new modules

AI model selector:
- AiAssistantService::MODEL_DEFAULTS and MODEL_OPTIONS const tables (3 picks per
  provider: Claude Opus 4.7 / Sonnet 4.6 / Haiku 4.5, OpenAI 4o / 4o-mini,
  Gemini 1.5 Pro / Flash). Default upgraded from Sonnet 4.5 → Sonnet 4.6.
- modelFor(provider, company?) resolves tenant override > global default.
- All 8 hardcoded model strings replaced with modelFor() across callClaude
  (chat with tool-use), callOpenAI, callGemini (chat), postClaude/postOpenAI/
  postGemini (single-shot), and OcrInvoiceService.
- Settings page adds 3 model selectors per provider with persistence at
  settings.ai.models.{claude,gpt,gemini}.

i18n nav labels:
- TireSet / Bodyshop / Subcontractor / SubcontractJob / PricingCoefficient /
  ShopCustomer resources: getNavigationLabel / getNavigationGroup /
  getModelLabel / getPluralModelLabel return __()-wrapped strings.
- 20 keys added to lang/ru.json and lang/en.json.

Tests (4 new): default model, tenant override wins, unknown provider falls
back to claude default, options dictionary contains each default key.

Full suite: 134 passed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/Services/Ai/OcrInvoiceService.php

@@ -52,7 +52,7 @@ class OcrInvoiceService
             ])
             ->timeout(60)
             ->post('https://api.anthropic.com/v1/messages', [
-                'model' => 'claude-sonnet-4-5',
+                'model' => app(AiAssistantService::class)->modelFor('claude', $company),
                 'max_tokens' => 2048,
                 'system' => $this->systemPrompt(),
                 'messages' => [[