feat: add showContent and hideContent public API

[yyjim]

Description

• Add showContent() and hideContent() public methods to CBLoggerWindow, complementing the existing toggleContent() for explicit control over the console panel visibility.
• Fix Action.handler stored property type to include @MainActor, aligning it with the init parameter signature.
• Update demo app with "Show Console" and "Hide Console" buttons to exercise the new API.

Test Plan

• Demo project can be built
• Tap "Show Console" — console panel appears
• Tap "Hide Console" — console panel hides
• "Toggle Console" still works as before
• Verify no warnings from @MainActor mismatch on Action.handler

Checklist

• Demo project can be built

Screenshots

Before	After