feat(site): add AI task status to deployment banner

Summary

Adds AI task statistics display to the Coder homepage deployment banner, showing active, completed, and failed AI task counts. This implements both the backend API (/api/experimental/aitasks/stats) and frontend integration to surface AI agent activity to users.

Key Components:

• Backend: New experimental API endpoint with Go struct definitions
• Frontend: Integration with deployment banner, respects CODER_HIDE_AI_TASKS configuration
• UI: Clean display with tooltips and icons matching existing banner style

Review & Testing Checklist for Human

• CRITICAL: Verify hardcoded mock data approach - Backend currently returns fixed values (3 active, 15 completed, 2 failed). Confirm this is acceptable for demo/testing purposes and understand timeline for real data integration
• Test actual UI rendering - Load Coder dashboard and verify AI stats appear correctly in deployment banner with proper styling and tooltips
• Verify configuration hiding works - Test that setting CODER_HIDE_AI_TASKS=true properly hides the AI stats section
• Manual API testing - Hit /api/experimental/aitasks/stats directly to confirm endpoint works and returns expected JSON structure
• Check TypeScript type generation - Verify CI properly generates AITasksStatsResponse type (I manually added it due to local Go version issues)

Recommended Test Plan:

1. Start local Coder instance and navigate to homepage
2. Verify AI stats appear in deployment banner
3. Test with CODER_HIDE_AI_TASKS=true to confirm hiding
4. Check browser network tab for successful API calls
5. Verify tooltips and responsive design work properly

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    Backend["codersdk/aitasks.go<br/>AITasksStatsResponse struct"]:::major-edit
    Handler["coderd/aitasks.go<br/>aiTasksStats handler"]:::major-edit  
    Routes["coderd/coderd.go<br/>Route registration"]:::minor-edit
    
    
    API["site/src/api/api.ts<br/>getAITasksStats method"]:::major-edit
    Query["site/src/api/queries/aitasks.ts<br/>Query helper"]:::major-edit
    Banner["site/src/modules/dashboard/<br/>DeploymentBanner.tsx"]:::major-edit
    BannerView["site/src/modules/dashboard/<br/>DeploymentBannerView.tsx"]:::major-edit
    Types["site/src/api/typesGenerated.ts<br/>TypeScript types"]:::minor-edit
    
    Backend --> Handler
    Handler --> Routes
    Backend --> Types
    Types --> API
    API --> Query  
    Query --> Banner
    Banner --> BannerView
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit  
        L3[Context/No Edit]:::context
    end

classDef major-edit fill:#90EE90
classDef minor-edit fill:#87CEEB  
classDef context fill:#FFFFFF

Notes

• Environment Issues: Local Go version (1.18) incompatible with project requirements (1.24), preventing full local testing and type generation
• Mock Data: Backend uses hardcoded statistics for demonstration - needs real AI task tracking integration
• Session Details: Implemented by @devin for @bpmct, session: https://app.devin.ai/sessions/0279d5b7f7d6495cadaf926f293e3465
• CI Status: All technical checks passing except CLA (administrative issue)