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>

clubmanager/settings.py

@@ -43,8 +43,12 @@ INSTALLED_APPS = [
     "django.contrib.sessions",
     "django.contrib.messages",
     "django.contrib.staticfiles",
+    "phonenumber_field",
+    "accounts",
 ]
 
+AUTH_USER_MODEL = "accounts.User"
+
 MIDDLEWARE = [
     "django.middleware.security.SecurityMiddleware",
     "django.contrib.sessions.middleware.SessionMiddleware",
@@ -123,3 +127,9 @@ STATICFILES_DIRS = [BASE_DIR / "static"]
 
 MEDIA_URL = "media/"
 MEDIA_ROOT = BASE_DIR / "media"
+
+
+# Phone numbers (django-phonenumber-field)
+
+PHONENUMBER_DEFAULT_REGION = "BE"
+PHONENUMBER_DB_FORMAT = "E164"