Create API Client

[orhantugrul]

Create API client utilities for dashboard to communicate with backend.

• Create dashboard/lib/api.ts with base URL and fetch wrapper
• Create dashboard/lib/api/stats.ts with stats API functions
• Create dashboard/.env.local.example with API URL
• Update dashboard/.gitignore to exclude .env.local

Acceptance Criteria

• API client handles errors properly
• All stats functions are type-safe
• Environment variable is configurable