Add TypeScript + Express + Postgres backend with Better Auth

Implements the first temetro backend: an Express 5 API on Postgres via
Drizzle ORM, with authentication and multi-tenant clinics powered by
Better Auth.

- Auth: email/password with required email verification, password reset,
  rate limiting, CSRF/trusted-origins, secure cookies, session audit hook.
- Organizations (clinics) with RBAC (owner/admin/member/viewer) and an
  extended `patient` permission set; member invitations by email.
- Org-scoped patient records mirroring the frontend Patient shape, with
  CRUD endpoints gated by permission (read/write/delete).
- Email helper logs links to the console when SMTP is unset (zero-setup
  local dev); Dockerfile + docker-compose (db + backend + frontend) with
  migrations applied on startup and a configurable Postgres host port.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/.gitignore

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+node_modules
+dist
+.env
+.env.local
+*.log
+npm-debug.log*
+.DS_Store
+coverage