Update admin theme/layout and refresh README details.

Align the project baseline with the latest admin interface styling and layout structure while documenting setup and usage updates in README.

apps/api/app/modules/users/service.py

@@ -0,0 +1,29 @@
+from app.core.security import hash_password, verify_password
+from app.modules.auth.service import revoke_user_refresh_family
+from app.modules.media.service import upload_user_avatar
+from app.modules.users import repository
+from app.modules.users.models import User
+
+
+def get_me(user: User) -> dict:
+    profile = repository.get_profile(user.id)
+    return {"user": user, "profile": profile}
+
+
+def update_me(user: User, display_name: str | None) -> dict:
+    profile = repository.update_profile(user.id, display_name=display_name)
+    return {"user": user, "profile": profile}
+
+
+def upload_avatar(user: User, content: bytes) -> dict:
+    avatar_url = upload_user_avatar(user.id, content)
+    profile = repository.update_profile(user.id, avatar_url=avatar_url)
+    return {"user": user, "profile": profile}
+
+
+def change_password(user: User, current_password: str, new_password: str) -> None:
+    if not verify_password(current_password, user.password_hash):
+        raise ValueError("INVALID_CURRENT_PASSWORD")
+    user.password_hash = hash_password(new_password)
+    repository.update_user(user)
+    revoke_user_refresh_family(user.id)