Prompt 2 — Profiles

Implement user profiles:

• GET /api/profiles/:username
• POST /api/profiles/:username/follow (auth required)
• DELETE /api/profiles/:username/follow (auth required)

Write tests for all three endpoints.

---

Before committing: run the Verification Protocol (see CLAUDE.md § Verification Protocol). All 7 steps must pass. Do not commit a partial green state.