build(frontend): sweep every stylesheet, not index.css by name

The hook fires on frontend/**/*.{ts,css} while the script read one hardcoded path, so a second stylesheet would have been silently unswept while the hook still went green over it. There is only index.css today, which is exactly when this is cheap to fix. Watched catching a planted nested rule in a second file.

CLAUDE.md

@@ -3502,7 +3502,10 @@ would notice on 113 — the rule simply does not exist, there and nowhere
 else, which is how the bottom bar's `text-overflow: ellipsis` came to
 have never truncated on the device. `make css-check`
 (`frontend/scripts/check-css-nesting.mjs`, a pre-commit hook and a CI
-step) fails on one, over `index.css` and the `css` literals alike, and
+step) fails on one, over every `frontend/*.css` and the `css` literals
+alike — a glob rather than `index.css` by name, because the hook fires
+on `frontend/**/*.{ts,css}` and a sweep that names one file goes green
+over a stylesheet it never opened — and
 says the fix is a leading `&` — valid in both syntaxes, so no nested
 rule here has a reason to omit it. Two things it has to get right, and
 both follow from asking whether a *style* rule is anywhere above rather

frontend/scripts/check-css-nesting.mjs

@@ -18,10 +18,24 @@ import { findBareNestedRules } from './css-nesting.mjs';
 
 const problems = [];
 
-for (const { line, selector } of findBareNestedRules(
-  readFileSync('index.css', 'utf8'),
-)) {
-  problems.push({ file: 'index.css', line, selector });
+// Every stylesheet, not `index.css` by name: the hook that runs this
+// fires on `frontend/**/*.{ts,css}`, so naming one file promises a
+// coverage the sweep does not deliver -- a second stylesheet would be
+// silently unswept while the hook still went green over it. There is
+// only `index.css` today, which is exactly when this is free to fix.
+const stylesheets = globSync('*.css', { cwd: process.cwd() });
+
+if (stylesheets.length === 0) {
+  console.error('css-nesting-check: no stylesheet matched *.css');
+  process.exit(1);
+}
+
+for (const file of stylesheets) {
+  for (const { line, selector } of findBareNestedRules(
+    readFileSync(file, 'utf8'),
+  )) {
+    problems.push({ file, line, selector });
+  }
 }
 
 const sources = globSync('src/**/*.ts', { cwd: process.cwd() });
@@ -61,5 +75,5 @@ if (problems.length > 0) {
 }
 
 console.log(
-  `css-nesting-check: index.css + ${sources.length} files, no bare nested rules`,
+  `css-nesting-check: ${stylesheets.length} stylesheet(s) + ${sources.length} files, no bare nested rules`,
 );