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/widget/flex/mod.rs

@@ -4,16 +4,19 @@
 use crate::render::Canvas;
 use super::Element;
 
-/// Wraps an [`Element`] so that a [`Row`](crate::layout::row::Row) treats it
-/// like a [`Spacer`](crate::layout::spacer::Spacer) for leftover-width
-/// distribution, but draws the child inside the allocated rect.
+/// Wraps an [`Element`] so its parent treats it like a
+/// [`Spacer`](crate::layout::spacer::Spacer) for leftover-space
+/// distribution, but draws the child inside the allocated rect: leftover
+/// **width** inside a [`Row`](crate::layout::row::Row), leftover
+/// **height** inside a [`Column`](crate::layout::column::Column).
 ///
-/// Use this to make a non-trivial child fill remaining width without resorting
-/// to a hard-coded `max_width`. The row computes how much width is left after
-/// the fixed-size siblings, splits it across all flex / spacer children
-/// proportionally to their `weight`, and gives the flex its share. The wrapped
-/// child sees that share as its layout rect — text inside it triggers its own
-/// elide path on overflow, columns adjust their inner width, etc.
+/// Use this to make a non-trivial child fill remaining space without
+/// resorting to a hard-coded size. The parent computes how much of its
+/// main axis is left after the fixed-size siblings, splits it across all
+/// flex / spacer children proportionally to their `weight`, and gives
+/// the flex its share. The wrapped child sees that share as its layout
+/// rect — text inside it triggers its own elide path on overflow,
+/// columns adjust their inner width, etc.
 ///
 /// ```rust,no_run
 /// # use ltk::{ column, flex, row, Element };
@@ -30,10 +33,6 @@ use super::Element;
 /// # }
 /// ```
 ///
-/// Currently only [`Row`](crate::layout::row::Row) honours flex distribution.
-/// Inside a [`Column`](crate::layout::column::Column) a flex child behaves
-/// like a regular zero-width child along the main axis — vertical flex is not
-/// yet implemented.
 pub struct Flex<Msg: Clone>
 {
 	pub( crate ) child:  Box<Element<Msg>>,
@@ -51,9 +50,9 @@ impl<Msg: Clone> Flex<Msg>
 		}
 	}
 
-	/// Relative weight when sharing leftover width with other flex / spacer
-	/// children in the same row (default `1`). A flex with `weight = 2`
-	/// claims twice the space of a sibling with `weight = 1`.
+	/// Relative weight when sharing leftover space with other flex / spacer
+	/// children in the same row or column (default `1`). A flex with
+	/// `weight = 2` claims twice the space of a sibling with `weight = 1`.
 	pub fn weight( mut self, w: u32 ) -> Self
 	{
 		self.weight = w;