Titlebar Disable Toggle

[plyght]

This pull request adds a new configuration option to control the visibility of the session titlebar in the TUI, and updates the UI to display context and cost information in the prompt area when the titlebar is hidden. It also includes minor refactoring and type imports to support these changes.

TUI Titlebar Visibility and Context/Cost Display:

• Added a titlebar boolean configuration option to the TUI settings in config.ts, allowing users to show or hide the session titlebar. [1] [2]
• Updated the session route to only render the Header component (titlebar) when both the sidebar is hidden and the titlebar setting is enabled. [1] [2]
• Modified the prompt component to display context and cost information in the prompt area when the titlebar is hidden, including logic to compute and format these values. [1] [2] [3] [4]

Titlebar Enabled (Default):

Titlebar Disabled: