fix(web): style editor no longer strands leaf-valued layout fields

A prior fix on this PR made elementKeys() append any layout-only key with
no style block of its own (a logo, a timeout indicator, a possession
arrow), so table() draws a row for it instead of losing it when the
wholesale `layout` claim removes the generic fallback. That covers a
layout-only key shaped like an object (x_offset/y_offset, ...), because
columnsFor() only ever produced columns from a key's *sub-fields*.

It missed the case where the layout-only key's own value is itself a
leaf -- a plain "show_logo" boolean directly under layout, no x/y object
underneath. elementKeys() still lists it (any row: no matching column),
so it renders as an uneditable blank row and its only control -- the
generic fallback checkbox -- is still gone. Confirmed by executing the
real widget's render() against a synthetic schema in Node (a DOM-stub
harness, not committed): the field's name never appeared as an <input>.

columnsFor() now gives such a leaf key a column keyed to itself
('layout-leaf'), and elementRow() binds it to the leaf's own path
(customization.layout.<key>, matching the name the fallback would have
used) instead of leaving every cell blank.

New regression test (test/js/unit/test_style_editor_layout_leaf_columns.js,
following this PR's existing eval-extraction pattern) checks the leaf
column is produced, is self-keyed, doesn't duplicate, and that a schema
with no leaf-valued layout key is unaffected; wired into run_all.js and
the suite table in test/js/README.md.

test/js/run_all.js: 84 + 6 + 6 = all suites passed (jsdom unavailable
here, DOM suites skip as before). Python suite untouched by this change;
test_style_editor_extra_fields.py, test_style_editor_save_roundtrip.py
and the one PIL-dependent style_editor_takeover.py case fail identically
before this commit -- missing flask/PIL in this sandbox, not this PR.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

test/js/unit/test_style_editor_layout_leaf_columns.js

@@ -0,0 +1,89 @@
+// Regression test for style-editor.js's columnsFor(), extracted verbatim
+// from the shipped widget (own/ownObj/elementKeys/columnsFor have no DOM
+// dependency) so the test can't drift from the real implementation.
+//
+// elementKeys() already appends a layout-only key that never got its own
+// top-level style block (see test_style_editor_element_keys.js), so table()
+// draws a row for it. But render() still claims the whole `layout` child as
+// the widget's own regardless of what that row actually shows -- and
+// columnsFor() only produced a column for a layout-only key whose own value
+// is an *object* with sub-fields (x_offset, y_offset, ...). A hand-written
+// schema can instead put a plain leaf value directly under layout -- a
+// "show_logo" toggle, a timeout indicator's on/off flag -- with no x/y
+// object underneath it. That key still got a row (data-element="show_logo"),
+// but zero columns ever matched it, so the row rendered with every cell
+// blank: no control, and no way back to the fallback since layout was
+// removed wholesale. This pins the fix: such a key gets its own
+// self-keyed 'layout-leaf' column.
+const fs = require('fs');
+const path = require('path');
+const V3 = path.resolve(__dirname, '../../../web_interface/static/v3');
+
+const src = fs.readFileSync(path.join(V3, 'js/widgets/style-editor.js'), 'utf8');
+const start = src.indexOf('function own(obj, key)');
+const endMark = 'function control(opts)';
+const end = src.indexOf(endMark);
+if (start === -1 || end === -1) {
+  console.error('FAIL: could not locate own()/columnsFor() in style-editor.js -- slice markers need updating');
+  process.exit(1);
+}
+eval(src.slice(start, end)); // defines own/ownObj/elementKeys/columnsFor
+
+let failures = 0;
+function ok(desc, cond) {
+  if (cond) { console.log(`ok - ${desc}`); }
+  else { console.log(`FAIL - ${desc}`); failures++; }
+}
+
+// score_text is a real style element; possession is layout-only but shaped
+// like an object (x/y); show_logo is layout-only and a bare leaf value.
+const schema = {
+  properties: {
+    score_text: {
+      type: 'object',
+      'x-style-managed': true,
+      properties: { font: { type: 'string' }, text_color: { type: 'array' } },
+    },
+    layout: {
+      type: 'object',
+      properties: {
+        score_text: { type: 'object', properties: { x_offset: {}, y_offset: {} } },
+        possession: { type: 'object', properties: { x_offset: {}, y_offset: {} } },
+        show_logo: { type: 'boolean', default: true },
+      },
+    },
+  },
+};
+
+const columns = columnsFor(schema);
+const byKey = {};
+columns.forEach(function (c) { byKey[c.key] = c; });
+
+ok('an element style field still gets its own column', byKey.font && byKey.font.where === 'element');
+ok('a layout-only object key still contributes its x/y columns',
+   byKey.x_offset && byKey.x_offset.where === 'layout');
+ok('a layout-only leaf key gets a column keyed to itself',
+   !!byKey.show_logo);
+ok('...marked as a layout-leaf column, not a shared sub-field',
+   byKey.show_logo && byKey.show_logo.where === 'layout-leaf');
+ok('nothing is duplicated', columns.length === new Set(columns.map(function (c) { return c.key; })).size);
+
+// A schema with no leaf-valued layout key must not gain a phantom column --
+// this is the common case (every existing scoreboard) and must be unaffected.
+const noLeaf = {
+  properties: {
+    score_text: {
+      type: 'object', 'x-style-managed': true,
+      properties: { font: { type: 'string' } },
+    },
+    layout: {
+      type: 'object',
+      properties: { score_text: { type: 'object', properties: { x_offset: {} } } },
+    },
+  },
+};
+ok('a schema with only object-shaped layout keys gets no layout-leaf column',
+   columnsFor(noLeaf).every(function (c) { return c.where !== 'layout-leaf'; }));
+
+if (failures) { console.log(`\n${failures} failure(s)`); process.exit(1); }
+console.log('\nall checks passed');