docs overhaul, orientation API, fluid-sizing fixes, examples made honest

Documentation pass: every claim in docs/ and the meta files was audited against the source and the drift fixed — around ninety corrections. CONTRIBUTING and the CI workflow now run cargo test with --features test-support (the gated test_support module made both the documented commands and the CI build fail to compile), make example becomes make examples, make doctest-md and the debhelper requirement of make clean are documented, and patch shape asks for a CHANGELOG entry. theming.md loses the nonexistent surface.backdrop, gains the real gradient defaults (linear-rgb, oklab), the six slot variants including typography, the ten-field palette, a truthful effects-consumer table, the ThemePreference/from_hour API and a responsive-sizing note; the stale docstrings in src/theme that fed the drift are fixed too. architecture.md's "Known gaps" section is rewritten against reality (multi-touch slots, xdg-activation, a11y live regions and SetValue/Increment/Decrement are implemented), gains a module map, subsurfaces and window-lifecycle coverage, and correct crustace/loginmanager paths. widgets.md fixes the ten factual errors (stateless spinner, toast/combo via overlays(), tooltip hover contract, row has no max_width, scroll axes, multiline text_edit, dialog panic wording) and now states the column() 16 px default padding — the recurring ambush — plus row's differing 0 default and dialog's max_width. onboarding, README and cookbook get the remaining sweep: build/test instructions, complete example lists, img_widget, clipping-parity honesty, ~30 Hz software cap, read_rgba_pixels signature, tab indentation in snippets, and rustdoc-style links that rendered literally are gone everywhere. CHANGELOG is restructured per Keep a Changelog with the missing entries (window_resizable, claims_raw_touch, Row::align_top/fill_height, caret fixes, dependency pins) and the pad_v Added/Changed contradiction resolved.
New adaptive-layout API: ltk::orientation() with the Orientation enum, backed by viewport_size()/set_viewport_size — the runtime records the main surface's physical dimensions on every configure, before App::on_resize, so view() can branch a layout on portrait vs landscape without hand-tracking resizes. The portrait rule matches Length::orient (square counts as portrait); embedders driving core::UiSurface call set_viewport_size themselves. Documented in the crate root's responsive-design section and architecture.md.
Fluid-vs-fixed sizing fixes in widgets, all the same disease — fluid content inside a fixed-pixel box. TextEdit::fixed_width takes impl Into<Length> (f32 call sites keep compiling as px) and the time picker's digit fields move to Length::fluid( 72.0 ), matching their fluid font so digits can no longer outgrow the box. Dialog::max_width takes impl Into<Length> with a Length::fluid( 480.0 ) default so the card scales with the stock buttons inside it, and the card's interior no longer stacks the column() default 16 px padding on top of CARD_PADDING — that double inset squeezed the action row until its buttons clipped on narrow windows. App::on_pointer_axis now triggers a view rebuild and repaint; previously state mutated in the hook did not paint until the next unrelated event.
Examples reworked to be honest demos: responsive's mode/density controls become stock buttons in a grid/column so they follow the modes they demonstrate instead of overflowing; dialog's openers stack vertically, and the example gains the app-level ESC handler so the ESC chain closes an open dialog first and quits second; widgets' tab strip now switches real per-tab pages; carousel gains pointer/touch drag through the horizontal-swipe hooks (crustace's pager pattern), one-tile-per-detent mouse wheel, and snap math driven by the real surface width from on_resize instead of a hardcoded 800; clip_path arranges its cells by ltk::orientation() and sizes them from the counter-axis of the flow.

examples/widgets.rs

@@ -75,15 +75,11 @@ impl App for WidgetsApp
 
 		let title = text( "ltk widgets" ).size( 24.0 ).color( primary ).align_center();
 
-		// Segmented tab strip — selection just rendered as a banner below.
+		// Segmented tab strip — each tab shows its own page below.
 		let tabs_strip: Element<Msg> = tabs( [ "General", "Audio", "Network" ] )
 			.selected( self.tab )
 			.on_select( Msg::SelectTab )
 			.into();
-		let tab_label = format!(
-			"Active tab: {}",
-			[ "General", "Audio", "Network" ][ self.tab.min( 2 ) ],
-		);
 
 		let toggles = column::<Msg>()
 			.spacing( 0.0 )
@@ -124,29 +120,44 @@ impl App for WidgetsApp
 			.id( WidgetId( "widgets/note" ) )
 			.on_change( Msg::NoteChanged );
 
+		// One page per tab, so selecting a tab visibly swaps the content.
+		let page: Element<Msg> = match self.tab.min( 2 )
+		{
+			0 => column::<Msg>()
+				.padding( 0.0 )
+				.spacing( 12.0 )
+				.push( toggles )
+				.push( separator() )
+				.push( checkboxes )
+				.push( separator() )
+				.push( radios )
+				.into(),
+			1 => column::<Msg>()
+				.padding( 0.0 )
+				.spacing( 12.0 )
+				.push( text( vol_label ).size( 13.0 ).color( secondary ) )
+				.push( slider( self.volume ).on_change( Msg::SliderChanged ) )
+				.push( text( prog_label ).size( 13.0 ).color( secondary ) )
+				.push( progress_bar( self.progress ) )
+				.into(),
+			_ => column::<Msg>()
+				.padding( 0.0 )
+				.spacing( 12.0 )
+				.push( text( "Spinner" ).size( 13.0 ).color( secondary ) )
+				.push( spin_row )
+				.push( separator() )
+				.push( text( "Multiline text edit" ).size( 13.0 ).color( secondary ) )
+				.push( textarea )
+				.into(),
+		};
+
 		let content = column::<Msg>()
 			.padding( 32.0 )
 			.spacing( 12.0 )
 			.push( title )
 			.push( tabs_strip )
-			.push( text( tab_label ).size( 13.0 ).color( secondary ) )
 			.push( separator() )
-			.push( toggles )
-			.push( separator() )
-			.push( checkboxes )
-			.push( separator() )
-			.push( radios )
-			.push( separator() )
-			.push( text( vol_label ).size( 13.0 ).color( secondary ) )
-			.push( slider( self.volume ).on_change( Msg::SliderChanged ) )
-			.push( text( prog_label ).size( 13.0 ).color( secondary ) )
-			.push( progress_bar( self.progress ) )
-			.push( separator() )
-			.push( text( "Spinner" ).size( 13.0 ).color( secondary ) )
-			.push( spin_row )
-			.push( separator() )
-			.push( text( "Multiline text edit" ).size( 13.0 ).color( secondary ) )
-			.push( textarea )
+			.push( page )
 			.push( spacer() )
 			.push(
 				text( "Esc = quit" )