Bump to 0.2.0: SW/GLES paint parity, shared font resolution, FrameState refactor, docs and packaging fixes

Rendering parity (software ↔ GLES). The software backend now rounds glyph pen positions and image destinations to the nearest integer pixel, matching what the GLES backend already did; previously it truncated, so text and 1:1 images could land up to half a pixel off between the two backends and the bilinear sample read ~1 px softer than the source. Gradients and shadows are deliberately left unimplemented on the software backend, and the GLES multi-rect `glScissor` clip is left coarse on purpose: making it exact would need stencil bits the EGL config does not carry, or routing the partial-redraw path through the offscreen clip layer, which would break its `fill` / `clear_rects_transparent` scissor semantics. Adds software-backend pixel tests covering the snapping.
Font resolution unification. The system-font candidate chain, `find_font_opt` and `load_default_font_bytes` lived in two copies (`render/helpers` and `gles_render/helpers`) that had already diverged — one resolved through `find_font_opt`, the other inlined the candidate loop — and now live once in `system_fonts`. The two per-backend `OnceLock` default-font caches and `primary_handle` collapse into a single `system_fonts::default_handle`. Module docs and the `font_registry` caller are updated accordingly.
Shared image validation and rect inflation. `draw_image_data`'s dimension check and its one-line warning were byte-duplicated across both backends and are now `render::helpers::validate_rgba_dims`. The six manual symmetric `Rect`-inflate literals in the GLES primitives reuse the existing `Rect::expand`.
FrameState and DrawCtx de-duplication. The eleven `SurfaceState` fields the draw pass owns and threads through `DrawCtx` — `widget_rects`, the cursor / selection maps, the scroll state, `accessible_extras`, `prev_focused` / `prev_hovered` / `prev_pressed` — move into a `FrameState` sub-struct. The per-frame `build_draw_ctx` / `commit_draw_ctx` helpers can then borrow `&mut ss.frame`, disjoint from `ss.canvas` and `ss.pool`, so the four frame paths (software / GLES × full / partial) replace their duplicated `DrawCtx` construction and write-back with a single helper call each. A whole-`SurfaceState` borrow could not express this (partial borrows do not cross function boundaries), which is why the helpers take the sub-struct. `content_dirty` stays on `SurfaceState` — it is an invalidation flag, not frame state — and is reset at the call site.
rich_text tests. Adds the previously-missing `tests.rs` for the `RichText` widget: one hit rect per visual line a link spans (the widget's core invariant), the single-line and no-link cases, preferred-size growth with hard line breaks, and `map_msg` range preservation — all headless against a software `Canvas`, with line counts forced by `\n` so they do not depend on any system font's measured width.
Documentation. Fills the rustdoc gaps on the embedder-facing surface: `core::UiSurface` accessors, the `egl_context` public API, the `GlesCanvas` methods, `theme::typography` and `theme::error`, and the `RichText` / `Text` builders; adds a crate-level "Rendering backends" overview. `CHANGELOG.md` is added (0.2.0 / 0.1.0), and `docs/widgets.md` / `docs/cookbook.md` gain `rich_text`, `external`, and the CPU-draw / path-clip / externally-laid-out-tree recipes. `debian/changelog` gets the 0.2.0-1 entry. Private intra-doc links to `system_fonts` are demoted to code spans so `cargo doc` is warning-free.
Packaging. The `libltk-dev` registry crate shipped a `Cargo.toml` declaring the `lookup` bench while the `Makefile` install copied only `src/`, so Cargo refused to parse the manifest over a missing `benches/lookup.rs`; the install now ships `benches/` as well (the file alone satisfies the parse — criterion is a dev-dependency and is not resolved when the crate is consumed as a library). `Cargo.toml` is bumped to 0.2.0 to match the package version and the `ltk-0.2.0` registry directory.

src/widget/text/mod.rs

@@ -1,6 +1,10 @@
 // SPDX-License-Identifier: LGPL-2.1-only
 // Copyright (C) 2026 Liberux Labs, S. L. <info@liberux.net>
 
+//! Single- or multi-line text: a font-sized, coloured, aligned string that
+//! either stays on one line (truncating with an ellipsis on overflow) or
+//! word-wraps to the layout width.
+
 use std::sync::Arc;
 
 use fontdue::Font;
@@ -13,14 +17,20 @@ use super::Element;
 #[ cfg( test ) ]
 mod tests;
 
+/// Horizontal alignment of text within its layout rect.
 #[ derive( Debug, Clone, Copy, PartialEq ) ]
 pub enum TextAlign
 {
+	/// Align to the left edge.
 	Left,
+	/// Centre within the rect.
 	Center,
+	/// Align to the right edge.
 	Right,
 }
 
+/// A run of text rendered with a size, colour, alignment and optional font,
+/// either word-wrapped or kept on one line with ellipsis truncation.
 pub struct Text
 {
 	pub content:  String,
@@ -45,6 +55,8 @@ pub struct Text
 
 impl Text
 {
+	/// A left-aligned, non-wrapping, ellipsis-truncated white label at the
+	/// default 16 px size with the canvas default font.
 	pub fn new( content: impl Into<String> ) -> Self
 	{
 		Self
@@ -68,6 +80,8 @@ impl Text
 		self.size.resolve( canvas.viewport_logical(), Length::EM_BASE_DEFAULT )
 	}
 
+	/// Paint the full string even when it overflows, instead of truncating
+	/// with an ellipsis.
 	pub fn no_truncate( mut self ) -> Self
 	{
 		self.truncate = false;
@@ -93,24 +107,28 @@ impl Text
 		self
 	}
 
+	/// Set the font size.
 	pub fn size( mut self, s: impl Into<Length> ) -> Self
 	{
 		self.size = s.into();
 		self
 	}
 
+	/// Set the text colour.
 	pub fn color( mut self, c: Color ) -> Self
 	{
 		self.color = c;
 		self
 	}
 
+	/// Set the horizontal alignment.
 	pub fn align( mut self, a: TextAlign ) -> Self
 	{
 		self.align = a;
 		self
 	}
 
+	/// Shorthand for [`Self::align`] with [`TextAlign::Center`].
 	pub fn align_center( mut self ) -> Self
 	{
 		self.align = TextAlign::Center;