Implements pansy's local (email + password) authentication and the session layer that OIDC (#5) will also reuse. - store: users.go (create/get-by-id/get-by-email/count) and sessions.go (create/get/touch/delete/delete-expired), scanning the existing 0001 schema. - service: the business-logic seam. auth.go (Register/Login/session lifecycle/Providers) + password.go (argon2id, 64 MiB/1/4, PHC-encoded, constant-time verify) + service.go (Service, clock injection, token hashing). First user is admin; closed registration still allows the bootstrap user; unknown-email and wrong-password are indistinguishable (same error, same argon2 work via a dummy hash). - api: POST /auth/register|login|logout, GET /auth/me|providers, plus a requireAuth middleware that resolves the HttpOnly session cookie (SameSite=Lax, Secure under https) to the actor. Handlers stay thin. - main: wires the service and a periodic expired-session sweep; sessions are also dropped lazily on access. Sliding 30-day expiry. - tests: service (register/login/expiry/renewal/cleanup, password) and api (cookie flow, middleware, validation, providers). Verified end-to-end via curl: register -> me -> restart -> session persists -> logout -> 401. Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]> Claude-Session: https://claude.ai/code/session_01JdQpdYYsTgtkJBxbcpAszi