docs: convert schema reference images to markdown tables

[Copilot]

Four schema reference tables existed only as embedded images — unsearchable, inaccessible to screen readers, and not renderable in non-GitHub contexts.

New file: SCHEMAS.md

Replaces all image-based schema tables with GitHub-flavored markdown, preserving the original 7-column structure (Key · JSON Key · JSON Type · Mandatory · Default · Accepted Values · Description) across all 8 sections:

• §1 TopBar Configuration Schema — id, version, tb_view_items
• §2 configurations Schema — number_of_tabs_in_ipad, number_of_tabs_in_iphone, supports_double_tap, supports_long_press, show_recently_accessed_module, margin
• §3 selected_tabs Schema — item_ids
• §4 item_organiser Root Schema — configurations, drop_down_view_items, quick_actions, profile
• §5 item_organiser.configurations.searchbar Schema — searchbar, visible_states
• §6 item_organiser.drop_down_view_items[] Schema — id, sections
• §6a item_organiser.drop_down_view_items[].sections[] Schema — id, item_ids
• §7 item_organiser.quick_actions Schema — action_ids, visible_states, item_style, item_alignment, layout, custom_grid_column_count
• §8 item_organiser.profile Schema — visible_states

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