Enables user selection for permissions

Replaces the user ID input field with a user selection dropdown,
allowing administrators to search and select users for permission
management. This simplifies the process of assigning permissions
and improves user experience.

Fetches Castle users via a new API endpoint and filters them
based on search input. Only users with Castle accounts
(receivables, payables, equity, or permissions) are listed.

views_api.py

@@ -1339,6 +1339,71 @@ async def api_get_all_users(
     return users
 
 
+@castle_api_router.get("/api/v1/admin/castle-users")
+async def api_get_castle_users(
+    wallet: WalletTypeInfo = Depends(require_admin_key),
+) -> list[dict]:
+    """
+    Get all users who have Castle accounts (receivables, payables, equity, or permissions).
+    This returns only users who are actively using Castle, not all LNbits users.
+    Admin only.
+    """
+    from lnbits.core.crud.users import get_user
+    from .crud import get_all_equity_eligible_users
+
+    # Get all user-specific accounts (Receivable/Payable/Equity)
+    all_accounts = await get_all_accounts()
+    user_accounts = [acc for acc in all_accounts if acc.user_id is not None]
+
+    # Get all users who have permissions
+    all_permissions = []
+    for account in all_accounts:
+        account_perms = await get_account_permissions(account.id)
+        all_permissions.extend(account_perms)
+
+    # Get all equity-eligible users
+    equity_users = await get_all_equity_eligible_users()
+
+    # Collect unique user IDs
+    user_ids = set()
+
+    # Add users with accounts
+    for acc in user_accounts:
+        user_ids.add(acc.user_id)
+
+    # Add users with permissions
+    for perm in all_permissions:
+        user_ids.add(perm.user_id)
+
+    # Add equity-eligible users
+    for equity in equity_users:
+        user_ids.add(equity.user_id)
+
+    # Build user list with enriched data
+    users = []
+    for user_id in user_ids:
+        # Get user details from core
+        user = await get_user(user_id)
+
+        # Use username if available, otherwise use user_id
+        username = user.username if user and user.username else None
+
+        # Get user's wallet setting if exists
+        user_wallet = await get_user_wallet(user_id)
+
+        users.append({
+            "id": user_id,
+            "user_id": user_id,  # Compatibility with existing code
+            "username": username,
+            "user_wallet_id": user_wallet.user_wallet_id if user_wallet else None,
+        })
+
+    # Sort by username (None values last)
+    users.sort(key=lambda x: (x["username"] is None, x["username"] or "", x["user_id"]))
+
+    return users
+
+
 @castle_api_router.get("/api/v1/user/wallet")
 async def api_get_user_wallet(
     user: User = Depends(check_user_exists),