Add accounts app: custom User, Member, families & guardianship

Introduce the foundational accounts app:
- Custom email-as-username User (AbstractBaseUser + PermissionsMixin) set
  as AUTH_USER_MODEL, decoupled from membership so children can be members
  without a login.
- Member model holding personal/roster data (names, contact email, phone +
  emergency phone via django-phonenumber-field, license number, DOB) with an
  optional link to a User.
- Family household grouping and directional Guardianship (guardian -> child)
  with uniqueness and no-self-guardian constraints.
- Custom UserAdmin plus Member/Family admin with inlines and autocomplete.
- Settings: register apps, AUTH_USER_MODEL, phonenumber defaults (BE/E164).
- Add CLAUDE.md and a tracked static/ directory.

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

pyproject.toml

@@ -5,6 +5,7 @@ requires-python = ">=3.14"
 dependencies = [
     "dj-database-url>=3.1.2",
     "django>=6.0.6",
+    "django-phonenumber-field[phonenumbers]>=8.4.0",
     "python-decouple>=3.8",
 ]