Drag the border between two columns to set their widths in 1.16.0

Umut, with a card of an icon next to a text as the example: "bei Rows die
Breite ändern, am besten per Drag and Drop im Editor". Rows only ever had
equal columns - both the classic `columns` token and the free `gridColumns`
produce `repeat(n, 1fr)`.

A row now carries the free style `columnWidths`, a list of shares such as
`2 1` or `66.7 33.3`, per device and without a new document schema.
`StyleCompiler::columnTracks()` turns it into `grid-template-columns`,
pads or cuts the shares to the number of columns, and gives a device whose
layout stacks the columns a single track, because the desktop rule carries
an id and would otherwise outrank the class that stacks a phone.

In the editor the border between two side-by-side columns of the selected
row is a handle: dragging restyles the row inline while the pointer moves
and writes one undo step on release; the arrow keys nudge by five points.
The design panel shows the same value as the text field "Spaltenbreiten".
The Playwright editor check drags the handle with the real mouse.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

public/assets/design-panel.js

@@ -248,6 +248,23 @@ export function createDesignPanel({ schema, onChange, onSavePreset, getBlock, ge
     return wrap;
   };
 
+  /**
+   * The column shares of a row, "2 1" for two thirds and a third. Dragging the border between two
+   * columns in the preview writes the same value; the field is for anyone who prefers numbers.
+   */
+  const fractionsControl = (id, value, apply) => {
+    const input = document.createElement('input');
+    input.type = 'text';
+    input.id = id;
+    input.value = value ?? '';
+    input.placeholder = 'gleich breit';
+    input.pattern = String.raw`\d{1,3}(\.\d)?( \d{1,3}(\.\d)?){0,11}`;
+    input.setAttribute('inputmode', 'decimal');
+    input.title = 'Anteile je Spalte, durch Leerzeichen getrennt: 2 1 oder 25 50 25';
+    input.addEventListener('change', () => { if (input.checkValidity()) apply(input.value.trim()); });
+    return input;
+  };
+
   const numberControl = (id, value, property, apply) => {
     const wrap = element('div', 'number-control');
     const slider = document.createElement('input');
@@ -531,6 +548,7 @@ export function createDesignPanel({ schema, onChange, onSavePreset, getBlock, ge
         else if (property.type === 'choice') control = choiceControl(id, own ? current.value : '', property, apply, inheritedText);
         else if (property.type === 'font') control = fontControl(id, own ? current.value : '', apply, inheritedText);
         else if (property.type === 'media') control = mediaControl(key, current.value || '', apply);
+        else if (property.type === 'fractions') control = fractionsControl(id, own ? current.value : '', apply);
         else continue;
 
         body.append(row(id, property.label, control, { own, inherited: inheritedText, onReset, chips: deviceChips(block, key, property.label, false) }));