docs: Convert Root Schema image to markdown table in README

[Copilot]

The Root Schema reference was only available as an image, making it unsearchable, inaccessible, and impossible to render in non-image contexts.

Changes

• README.md: Replaced the image-based Root Schema with a native markdown table under a new ## 1) Root Schema section

Key	JSON Key	JSON Type	Mandatory	Default	Accepted Values	Description
ID	id	String	✅ Yes	—	Any non-empty string (e.g., TAB_BAR_CONFIG)	Unique identifier for the tab bar configuration.
Version	version	String	✅ Yes	—	Version string (e.g., 1.0)	Schema/config version.
Configurations	configurations	Object	✅ Yes	—	Object	Global tab bar behavior/settings container.
Selected Tabs	selected_tabs	Object	✅ Yes	—	Object	Defines the tabs selected for the bar.
Item Organiser	item_organiser	Object	✅ Yes	—	Object	Organises dropdown, quick actions, profile, and related behavior.

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