layout: adaptive grid and vertical flex; enforce the mechanical style rules

grid_min_cell( width ) adds the adaptive mode WrapGrid was missing: instead of a fixed column count, the count is derived at layout time from the available width so every cell is at least `width` wide (any Length, so a fluid threshold works; never fewer than one column), re-derived on every resize. Cells then share the width equally, and WrapGrid::max_columns( n ) caps the derived count so cells grow instead of multiplying on very wide surfaces — the cap only applies to the adaptive mode, grid( n ) keeps the fixed behaviour untouched. Four new layout tests cover width derivation, spacing accounting, the one-column floor and the cap; the row-wrap assertions check X positions rather than Y because zero-height spacer children produce zero-height rows.
flex( child ) now distributes leftover height inside a Column, mirroring its leftover-width behaviour in a Row: flex children join the weight pool alongside weight-only spacers and y-scrolls, draw their child inside the allocated share at full inner width, and contribute zero to the column's natural height exactly like a row counts flex width. This closes the documented "vertical flex is not yet implemented" gap; the Flex rustdoc and the widgets.md entry now describe both axes.
Add scripts/style-check.sh and a make stylecheck target, wired into CI: mechanical verification of the grep-checkable subset of code_style_guide.md — tab indentation and spaces inside attribute brackets — with comment lines skipped so prose may cite raw attribute syntax. To turn the check on green, the 82 unspaced attribute sites across 24 files (#[test], #[derive(...)], #[cfg(...)], #[allow(...)]) were normalized to the spaced form. CONTRIBUTING and the style guide reference the new target; brace placement and paren spacing remain review concerns.

src/app.rs

@@ -23,7 +23,7 @@ pub enum ToplevelEvent
 }
 
 /// Wayland shell mode for the application surface.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[ derive( Debug, Clone, Copy, PartialEq, Eq ) ]
 pub enum ShellMode
 {
 	/// Normal application window using xdg-shell protocol.
@@ -41,7 +41,7 @@ pub enum ShellMode
 }
 
 /// Layer-shell layer position.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[ derive( Debug, Clone, Copy, PartialEq, Eq ) ]
 pub enum Layer
 {
 	/// Below normal windows (wallpapers, desktop backgrounds).
@@ -72,7 +72,7 @@ impl Layer
 
 /// Layer-shell anchor edges.
 /// Determines which screen edges the surface is attached to.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[ derive( Debug, Clone, Copy, PartialEq, Eq ) ]
 pub struct Anchor
 {
 	pub top:    bool,
@@ -115,13 +115,13 @@ impl Anchor
 /// overlay list between frames: if the same `OverlayId` is returned from
 /// [`App::overlays`] on consecutive frames the underlying Wayland surface
 /// and its internal state are kept; if it disappears the surface is destroyed.
-#[derive( Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord )]
+#[ derive( Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord ) ]
 pub struct OverlayId( pub u32 );
 
 /// Stable identifier for a subsurface, used to diff the list returned by
 /// [`App::subsurfaces`] between frames the same way [`OverlayId`] diffs
 /// overlays.
-#[derive( Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord )]
+#[ derive( Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord ) ]
 pub struct SubsurfaceId( pub u32 );
 
 /// Which surface a [`SubsurfaceSpec`] is composited as a child of. `Main`
@@ -129,7 +129,7 @@ pub struct SubsurfaceId( pub u32 );
 /// parents to one of the [`App::overlays`] surfaces, so a slide can ride
 /// above app windows the way an overlay panel does. An `Overlay` parent that
 /// is absent or not yet configured is skipped for that frame.
-#[derive( Debug, Clone, Copy, PartialEq, Eq )]
+#[ derive( Debug, Clone, Copy, PartialEq, Eq ) ]
 pub enum SubsurfaceParent
 {
 	Main,
@@ -138,7 +138,7 @@ pub enum SubsurfaceParent
 
 /// One of the surfaces an [`App`] can target with an invalidation. Used inside
 /// [`InvalidationScope::Only`] to name the affected surfaces.
-#[derive( Debug, Clone, Copy, PartialEq, Eq, Hash )]
+#[ derive( Debug, Clone, Copy, PartialEq, Eq, Hash ) ]
 pub enum SurfaceTarget
 {
 	/// The application's main surface (the one returned by [`App::view`]).
@@ -153,7 +153,7 @@ pub enum SurfaceTarget
 /// to let the runtime skip redraws on surfaces whose contents could not
 /// possibly have changed by the message in question. On a shell with many
 /// overlays most messages only touch one of them, so the savings are large.
-#[derive( Debug, Clone )]
+#[ derive( Debug, Clone ) ]
 pub enum InvalidationScope
 {
 	/// Treat every surface as potentially affected (safe default).