API wrapper baseline coverage

[ArchILLtect]

Area / Component

api.ts: buildUrl/normalizeJoin, api

Test Cases

• buildUrl passes through absolute URLs (e.g., https://example.com/x)
• returns parsed JSON on success (GET /api/me)
• returns text when response is not JSON (GET /api/version)
• throws with structured cause on error JSON (POST /api/auth/login; assert message and err.cause)

Target Release

0.2.1