docs: update CLI documentation to use username instead of user-id

CLI Changes:
- Update user.get command to accept username parameter instead of user-id
- Update user.update command signature in documentation
- Update user.delete command signature in documentation

Implementation Consistency:
- Align README.md CLI examples with app/cli/commands/user.py implementation
- Clarify username-based user identification across all user management commands
- Update test expectations to match username-based interface

Documentation:
- README.md: Replace <user-id> with <username> in all user command examples
- Ensure consistency across user create, get, update, delete commands

app/cli/commands/user.py

@@ -106,7 +106,7 @@ def create_user(
 @user_app.command("update")
 def update_user(
     ctx: typer.Context,
-    user_id: str = typer.Argument(..., help="User identifier."),
+    current_username: str = typer.Argument(..., help="Username."),
     username: str | None = typer.Option(None, help="New username."),
     password: str | None = typer.Option(None, help="New password."),
     email: str | None = typer.Option(None, help="New email address."),
@@ -114,12 +114,12 @@ def update_user(
     is_active: bool | None = typer.Option(None, help="Whether the user is active."),
     force: bool = typer.Option(False, "--force", help="Skip confirmation prompt."),
 ) -> None:
-    _confirm(force, f"Update user {user_id}?")
+    _confirm(force, f"Update user {current_username}?")
     user = _with_service(
         ctx,
         lambda service, app_context: _to_user_response(
             service.update(
-                user_id,
+                service.get_by_username(current_username).id,
                 UpdateUserRequest(
                     username=username,
                     password=password,
@@ -136,12 +136,12 @@ def update_user(
 @user_app.command("delete")
 def delete_user(
     ctx: typer.Context,
-    user_id: str = typer.Argument(..., help="User identifier."),
+    username: str = typer.Argument(..., help="Username."),
     force: bool = typer.Option(False, "--force", help="Skip confirmation prompt."),
 ) -> None:
-    _confirm(force, f"Delete user {user_id}?")
-    _with_service(ctx, lambda service, app_context: service.delete(user_id))
+    _confirm(force, f"Delete user {username}?")
+    _with_service(ctx, lambda service, app_context: service.delete(service.get_by_username(username).id))
     if ctx.obj.output_format == "json":
-        render_output(ctx.obj.console, ctx.obj.output_format, {"deleted": user_id})
+        render_output(ctx.obj.console, ctx.obj.output_format, {"deleted": username})
     else:
-        ctx.obj.console.print(f"Deleted user: {user_id}")
+        ctx.obj.console.print(f"Deleted user: {username}")