v0.2.0 — Accounts & Sign-In — Apple/Google auth

Accounts & Sign-In — Apple/Google auth

• feat: implement email/password auth with JWT access + refresh tokens
• feat: add Sign in with Apple via JWKS identity-token verification
• feat: add Google Sign-In with server-side id_token verification and account linking
• feat: build SwiftUI auth flow with Apple/Google coordinators and Keychain session