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

dist/tokens.css

@@ -0,0 +1,70 @@
+/* @bchen/ui v0.1.0 — semantic token palette
+ * Canonical light + dark values extracted from the bchen.dev fleet.
+ * Source of truth: inventory (cross-checked against authd, buchinese). */
+
+:root {
+  /* Primitive palette */
+  --black:    #000;
+  --white:    #fff;
+  --gray-50:  #fafafa;
+  --gray-100: #f0f0f0;
+  --gray-200: #e0e0e0;
+  --gray-400: #999;
+  --gray-600: #555;
+  --red:      #c00;
+
+  /* Typography */
+  --font:      -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
+  --font-mono: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+
+  /* Layout */
+  --radius:        0;
+  --header-height: 48px;
+
+  /* Border tokens */
+  --border-color:  var(--gray-200);
+  --border-strong: var(--black);
+  --border:        1px solid var(--border-strong);
+
+  /* Semantic color tokens */
+  --fg:           var(--black);
+  --fg-muted:     var(--gray-600);
+  --bg:           var(--white);
+  --bg-elevated:  var(--gray-50);
+  --surface:      var(--white);
+  --accent:       var(--black);
+  --accent-fg:    var(--white);
+  --accent-hover: var(--gray-600);
+  --danger:       var(--red);
+  --danger-fg:    var(--white);
+  --danger-bg:    #fff5f5;
+  --warning:      var(--gray-600);
+
+  /* Input tokens */
+  --input-bg:       var(--white);
+  --input-fg:       var(--black);
+  --input-border:   var(--black);
+  --input-bg-focus: var(--gray-50);
+}
+
+@media (prefers-color-scheme: dark) {
+  :root {
+    --bg:             #0f1115;
+    --bg-elevated:    #1a1d23;
+    --surface:        #0f1115;
+    --fg:             #e5e7eb;
+    --fg-muted:       #9ca3af;
+    --border-color:   #374151;
+    --border-strong:  #6b7280;
+    --accent:         #e5e7eb;
+    --accent-fg:      #0f1115;
+    --accent-hover:   #cbd5e1;
+    --danger:         #f87171;
+    --danger-fg:      #0f1115;
+    --danger-bg:      rgba(248, 113, 113, 0.12);
+    --input-bg:       #1a1d23;
+    --input-fg:       #e5e7eb;
+    --input-border:   #6b7280;
+    --input-bg-focus: #0f1115;
+  }
+}