refactor: centralize fixed theme variables

- move fixed font, navbar, and palette tokens to CSS-owned defaults
- replace check:css with Node test-runner helper and generation tests
- update contributor docs and PR build paths to use pnpm test

Author: evannotfound

.github/workflows/pr-build-check.yml

@@ -6,9 +6,13 @@ on:
       - main
       - dev
     paths:
+      - '_config.yml'
+      - 'layout/**'
+      - 'styles/**'
       - 'source/js/**'
       - 'source/css/**'
       - 'scripts/**'
+      - 'tests/**'
       - 'package.json'
       - 'pnpm-lock.yaml'
       - 'pnpm-workspace.yaml'
@@ -39,5 +43,8 @@ jobs:
           runtime: node@24
           cache: true
 
-      - name: Build Project
-        run: pnpm run build
+      - name: Test Theme
+        run: pnpm test
+
+      - name: Build JavaScript
+        run: pnpm run build:js

AGENTS.md

@@ -35,11 +35,11 @@ package-specific command says otherwise.
 ## Commands and verification
 
 - Install: `pnpm install --frozen-lockfile`.
-- Theme source or configuration: `pnpm run build`. There is no root test or
-  lint script; use `pnpm run build:css` or `pnpm run build:js` only for a
-  narrower affected area.
-- Theme CSS verification: `pnpm run check:css` builds CSS and generates the
-  canonical demo site with default, feature, and plugin configuration matrices.
+- Theme source or configuration: `pnpm run build`. Use `pnpm run build:css` or
+  `pnpm run build:js` only for a narrower affected area.
+- Theme tests: `pnpm test` uses Node's built-in test runner, builds CSS, tests
+  Hexo helpers, and generates the canonical demo site with default, feature,
+  and plugin configuration matrices.
 - Interactive theme preview: `pnpm dev` serves Hexo at
   `http://127.0.0.1:4000`, resets and links the demo site, and watches CSS.
   It serves source browser modules and does not watch production JavaScript