feat: add @bchen/ui v0.1.0 — dark-mode token palette and 16px base rule

- dist/tokens.css: canonical light + @media dark semantic-token palette
  extracted from inventory (cross-checked against authd and buchinese).
  Covers --fg, --fg-muted, --bg, --bg-elevated, --surface, --accent*,
  --danger*, --border*, --input-*, --warning, primitive --gray-* scale.
- dist/base.css: `input, textarea, select { font-size: 16px; }` prevents
  iOS Safari auto-zoom on focus.
- tests/tokens.test.ts: vitest — token presence in both light and dark
  blocks; WCAG AA contrast (>=4.5:1 body, >=3.0:1 UI) via inline
  hex-to-luminance math. All 10 tests green.
- tests/base.test.ts: vitest — asserts 16px rule covers all three selectors.
- .gitea/workflows/release.yml: tag-triggered CI — npm ci + npm test,
  CHANGELOG version gate, dist/scripts security grep, Gitea release
  artifact upload.
- README.md: four-step consumer integration guide with copy-pasteable
  snippets (package.json dep, Dockerfile cp, HTML link tags, app CSS).
- CHANGELOG.md: v0.1.0 entry.

npm audit --omit=dev: 0 vulnerabilities

Closes #1

vitest.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    environment: 'node',
+  },
+});