chore: add stylelint CSS linting and CI workflow

.github/workflows/lint.yml

@@ -0,0 +1,27 @@
+name: Lint
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+
+      - name: Install dependencies
+        run: npm install --no-audit --no-fund
+
+      - name: Lint CSS
+        run: npm run lint

.stylelintrc.json

@@ -0,0 +1,7 @@
+{
+  "extends": ["stylelint-config-standard"],
+  "rules": {
+    "custom-property-pattern": "^wm-",
+    "selector-class-pattern": null
+  }
+}

index.css

@@ -1,6 +1,6 @@
 /* Shared Wintermuted UI theme.
    Derived from the CV design language and generalized for app reuse. */
 
-@import "./styles/tokens.css";
-@import "./styles/base.css";
-@import "./styles/components.css";
+@import url("./styles/tokens.css");
+@import url("./styles/base.css");
+@import url("./styles/components.css");