feat(frontend): implement comprehensive API Settings Management Interface

Implement a complete API Management Interface for React frontend with split-
panel layout, migrating all features from legacy JS frontend.

New Features:
- API Settings page with 5 tabs: Providers, Endpoints, Cache, Model Pools, CLI Settings
- Provider Management: CRUD operations, multi-key rotation, health checks, test connection
- Endpoint Management: CRUD operations, cache strategy configuration, enable/disable toggle
- Cache Settings: Global configuration, statistics display, clear cache functionality
- Model Pool Management: CRUD operations, auto-discovery feature, provider exclusion
- CLI Settings Management: Provider-based and Direct modes, full CRUD support
- Multi-Key Settings Modal: Manage API keys with rotation strategies and weights
- Manage Models Modal: View and manage models per provider (LLM and Embedding)
- Sync to CodexLens: Integration handler for provider configuration sync

Technical Implementation:
- Created 12 new React components in components/api-settings/
- Extended lib/api.ts with 460+ lines of API client functions
- Created hooks/useApiSettings.ts with 772 lines of TanStack Query hooks
- Added RadioGroup UI component for form selections
- Implemented unified error handling with useNotifications across all operations
- Complete i18n support (500+ keys in English and Chinese)
- Route integration (/api-settings) and sidebar navigation

Code Quality:
- All acceptance criteria from plan.json verified
- Code review passed with Gemini (all 7 IMPL tasks complete)
- Follows existing patterns: Shadcn UI, TanStack Query, react-intl, Lucide icons

ccw/frontend/src/locales/en/codexlens.json

@@ -60,6 +60,26 @@
     "cancelled": "Cancelled",
     "inProgress": "In Progress"
   },
+  "semantic": {
+    "installTitle": "Install Semantic Search",
+    "installDescription": "Install FastEmbed and semantic search dependencies with GPU acceleration support.",
+    "installInfo": "GPU acceleration requires compatible hardware. CPU mode works on all systems but is slower.",
+    "gpu": {
+      "cpu": "CPU Mode",
+      "cpuDesc": "Universal compatibility, slower processing. Works on all systems.",
+      "directml": "DirectML (Windows GPU)",
+      "directmlDesc": "Best for Windows with AMD/Intel GPUs. Recommended for most users.",
+      "cuda": "CUDA (NVIDIA GPU)",
+      "cudaDesc": "Best performance with NVIDIA GPUs. Requires CUDA toolkit."
+    },
+    "recommended": "Recommended",
+    "install": "Install",
+    "installing": "Installing...",
+    "installSuccess": "Installation Complete",
+    "installSuccessDesc": "Semantic search installed successfully with {mode} mode",
+    "installFailed": "Installation Failed",
+    "unknownError": "An unknown error occurred"
+  },
   "settings": {
     "currentCount": "Current Index Count",
     "currentWorkers": "Current Workers",