#217 feat: refactor GET /api/artists to use auth-derived accountId

Summary

• Refactored GET /api/artists to use validateAuthContext → buildGetArtistsParams pattern (matching chats, pulses, sandboxes, organizations)
• Account ID is now derived from authentication — no more unauthenticated accountId query param
• No organization_id now returns personal artists only (was previously all artists)
• Removed personal query param (no longer needed)
• Added buildGetArtistsParams with 8 passing unit tests

Test plan

• pnpm test lib/artists/__tests__/buildGetArtistsParams.test.ts — 8/8 passing
• recoup artists list CLI returns personal artists
• curl -H "x-api-key: $KEY" ".../api/artists?organization_id=<uuid>" returns org artists
• curl ".../api/artists" returns 401

🤖 Generated with Claude Code