Fix maintenance mode API error handling and OpenAPI documentation

[Copilot]

The maintenance mode REST endpoints had ineffective error handling and incorrect OpenAPI schema annotations based on automated code review feedback.

Changes:

• Exception handling: Repository.getInstance().getComponent() throws IllegalArgumentException (doesn't return null), so replaced null checks with try-catch blocks to properly return error responses instead of 500s
• OpenAPI schema: Fixed @ApiResponse annotations to declare ReplyObject.class instead of Boolean.class to match actual return type
• Removed redundant operations: component.setMaintenanceMode() already updates the underlying ComponentConfig, so removed duplicate config.setMaintenanceMode() calls in enable/disable endpoints

// Before: ineffective null check
Component component = Repository.getInstance().getComponent(componentName);
if (component == null) {  // Never executed - getComponent() throws instead
    return ReplyObject.error("Component not found");
}

// After: proper exception handling
try {
    Component component = Repository.getInstance().getComponent(componentName);
    return ReplyObject.success("maintenanceMode", component.isMaintenanceMode());
} catch (IllegalArgumentException e) {
    return ReplyObject.error("Component not found: " + componentName);
}

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