Add Javadoc to 9 utility and integration classes (41 warnings fixed)

[Copilot]

Fixes 41 javadoc warnings across utility classes, event listeners, and third-party integration handlers. Part of broader effort to eliminate 400+ warnings blocking API documentation generation.

Files Modified

Core utilities:

• MiscUtils - Utility methods for date manipulation, broadcasting, metadata
• Layout - Book GUI layout rendering
• Listener<T> - Generic value request listener

Integration handlers:

• LoginSecurityLogin - LoginSecurity auth event listener
• ItemsAdderHandle - ItemsAdder custom item integration
• ItemModelHandler - Item model customization
• JavascriptEngineHandler - Cross-JVM Javascript engine management
• JavascriptPlaceholderRequest - Javascript placeholder abstraction

Effects:

• ItemMessage - Item tooltip-based popup messages

Key Pattern

Lombok's delombok generates getter/setter methods that inherit field-level javadoc. Field javadoc must include both @return and @param tags:

/**
 * BungeeCord channel name.
 * 
 * @return the bungee channel name
 * @param bungeeChannel the channel name to set
 */
@Getter
@Setter
private String bungeeChannel;

This generates:

public String getBungeeChannel() { ... }  // Inherits @return
public void setBungeeChannel(String bungeeChannel) { ... }  // Inherits @param

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