feat: implement full admin panel with dashboard, user management, and platform settings

Adds complete super_admin panel with 9 pages and account owner categories page.
Backend includes 5 new DB tables, ~25 API endpoints, settings manager with
in-memory cache, and 29 integration tests. Frontend includes reusable admin
components (DataTable, Pagination, ActionMenu, etc.) with code-split lazy loading.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/api/endpoints/admin.py

@@ -7,7 +7,9 @@ from sqlalchemy import select, func
 from app.core.database import get_db
 from app.core.audit import log_audit
 from app.models.user import User
+from app.models.account import Account
 from app.schemas.user import UserResponse, RoleUpdate, AccountRoleUpdate
+from app.schemas.admin import MoveUserAccount
 from app.api.deps import require_admin
 
 router = APIRouter(prefix="/admin", tags=["admin"])
@@ -167,3 +169,32 @@ async def activate_user(
     await db.commit()
     await db.refresh(user)
     return user
+
+
+@router.put("/users/{user_id}/move-account", response_model=UserResponse)
+async def move_user_account(
+    user_id: UUID,
+    data: MoveUserAccount,
+    db: Annotated[AsyncSession, Depends(get_db)],
+    current_user: Annotated[User, Depends(require_admin)],
+):
+    """Move a user to a different account (super admin only)."""
+    result = await db.execute(select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User not found")
+
+    result = await db.execute(select(Account).where(Account.display_code == data.display_code))
+    target_account = result.scalar_one_or_none()
+    if not target_account:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Target account not found")
+
+    old_account_id = user.account_id
+    user.account_id = target_account.id
+    user.account_role = "engineer"  # Reset to engineer on move
+
+    await log_audit(db, current_user.id, "user.move_account", "user", user.id,
+                    {"old_account_id": str(old_account_id), "new_account_id": str(target_account.id)})
+    await db.commit()
+    await db.refresh(user)
+    return user