Epic: Auth & Accounts (sign-up, login, verify email, forgot/reset password)

Stand up a real account system so the product is multi-user. Foundation for everything else.

Tracks (9):

• #45 — Auth: email/password sign-up (User entity in DynamoDB)
• #46 — Auth: login + session (signed cookie / JWT) + logout
• #47 — Auth: password hashing (argon2/bcrypt) + login throttling
• #48 — Auth: email verification (send token + verify endpoint)
• #49 — Auth: forgot-password (request reset email)
• #50 — Auth: reset-password (consume token, set new password)
• #51 — Auth: session lifecycle — expiry, refresh, "log out everywhere"
• #52 — Auth: account settings (change email w/ re-verify, change password)
• #53 — Auth: OAuth/SSO sign-in (Google + GitHub) [stretch]

Part of the Fathom + Sentry product backlog. See #44 for the original roadmap.

Epic complete — closed retroactively. All eight tracks (#45–#52) shipped: signup, JSON login + /me + logout, argon2id + login throttling, email verification, forgot/reset password (single-use tokens), sliding sessions + logout-all, account settings (name/password/email). #53 OAuth was scoped out as a stretch and remains open separately.