Issue 11: Wire frontend to backend

[SriMed]

Description

Replace placeholder functions with real API calls. Wire 'Load Example' to /example and 'Analyze' to /analyze. Render DiagnosticCard on success.

Implementation details

• lib/api.ts:
  • loadExample(domain: string): Promise<ExampleResponse>
  • analyzeExample(exampleId: string): Promise<AnalyzeResponse>
• Both POST to backend, URL from NEXT_PUBLIC_API_URL (default: http://localhost:8000)
• On loadExample success: populate preview card
• On analyzeExample success: render <DiagnosticCard result={response} />
• On any error: inline error message
• Disable relevant buttons during in-flight requests
• Create .env.local.example documenting all env vars

Acceptance criteria

• 'Load Example' populates preview card with real data
• 'Analyze' renders DiagnosticCard with real results
• Buttons disabled during in-flight requests
• Error message on non-200 or network failure
• Backend URL configurable via env var
• .env.local.example documented

TDD

frontend/__tests__/api.test.ts and page.test.tsx:

1. loadExample posts to /example with correct domain
2. analyzeExample posts to /analyze with correct example_id
3. Both return parsed responses on 200
4. Both throw on non-200
5. Preview card populates after loadExample
6. DiagnosticCard renders after analyzeExample
7. Buttons disabled during loading