Ratatui knowledge patch

Baseline: Ratatui through 0.28.x. Covered range: Ratatui 0.29.0 through 0.31.0.

Reference index

Reference	Topics
migration-and-configuration.md	MSRV, crate split, Cargo features, `no_std`, breaking migrations, Serde, prelude
layout-text-and-style.md	typed layout, flex, overlap, rectangles, text, styles, colors, borders
widgets-and-selection.md	tables, lists, tabs, scrollbars, sparklines, titles, calendars, reference widgets
charts-canvas-and-symbols.md	grouped bars, line gauges, canvas markers, clipping, layering, runtime symbols
terminal-backends-and-events.md	lifecycle, viewports, drawing, cursors, backend traits, event scheduling
architecture-state-and-testing.md	components, TEA, stateful rendering, templates, snapshots, safe buffers