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>

accounts/forms.py

@@ -0,0 +1,16 @@
+from django.contrib.auth.forms import BaseUserCreationForm
+from django.contrib.auth.forms import UserChangeForm as BaseUserChangeForm
+
+from .models import User
+
+
+class UserCreationForm(BaseUserCreationForm):
+    class Meta(BaseUserCreationForm.Meta):
+        model = User
+        fields = ("email",)
+
+
+class UserChangeForm(BaseUserChangeForm):
+    class Meta(BaseUserChangeForm.Meta):
+        model = User
+        fields = "__all__"