feat(frontend): Add AI Integration UI components
- Add aiApi client with types (ChatMessage, ChatRequest, ChatResponse, AIConfig, AIModel, AIUsageStats)
- Add useAI hooks (useAIConfig, useUpdateAIConfig, useAIModels, useAIChat, useAIUsage, useCurrentAIUsage, useAIHealth)
- Add AI components (AIChat, AISettings, ChatMessage)
- Add AIPage with chat interface and usage stats
- Add AI tab to Settings page
- Add AI Assistant link to dashboard navigation
- 979 lines added across 13 files
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>