feat: add sidebar and breadcrumb CSS exports

Closes #3

dist/breadcrumb.css

@@ -0,0 +1,45 @@
+/* @bchen/ui — breadcrumb navigation
+ * Uses only tokens defined in dist/tokens.css.
+ * Companion to dist/tokens.css and dist/base.css. */
+
+.breadcrumb {
+  display: flex;
+  align-items: center;
+  flex-wrap: wrap;
+  gap: 0.25rem;
+  padding: 0.75rem 2rem 0;
+  font-size: 13px;
+  color: var(--fg-muted);
+}
+
+.breadcrumb a {
+  color: var(--fg-muted);
+  text-decoration: none;
+}
+
+.breadcrumb a:hover {
+  color: var(--fg);
+  text-decoration: underline;
+  text-underline-offset: 2px;
+}
+
+.breadcrumb a:focus-visible {
+  color: var(--fg);
+  outline: 2px solid var(--accent);
+  outline-offset: 2px;
+  border-radius: 2px;
+}
+
+.breadcrumb [aria-current="page"] {
+  color: var(--fg);
+  font-weight: 500;
+  text-decoration: none;
+  cursor: default;
+}
+
+.breadcrumb-sep {
+  color: var(--fg-muted);
+  user-select: none;
+  font-size: 11px;
+  opacity: 0.6;
+}

dist/sidebar.css

@@ -0,0 +1,100 @@
+/* @bchen/ui — sidebar layout
+ * Uses only tokens defined in dist/tokens.css.
+ * Companion to dist/tokens.css and dist/base.css. */
+
+/* ── Desktop: two-column grid ─────────────────────────────────────────── */
+@media (min-width: 768px) {
+  body {
+    display: grid;
+    grid-template-columns: 200px 1fr;
+    grid-template-rows: 1fr;
+  }
+
+  .mobile-header { display: none; }
+
+  .sidebar {
+    display: flex;
+    flex-direction: column;
+    height: 100vh;
+    position: sticky;
+    top: 0;
+    border-right: var(--border);
+    background: var(--bg);
+    padding: 1rem 0;
+    overflow-y: auto;
+  }
+
+  .app-body {
+    min-width: 0;
+    display: flex;
+    flex-direction: column;
+    min-height: 100vh;
+  }
+}
+
+/* ── Mobile: sidebar hidden, top bar shown ─────────────────────────────── */
+@media (max-width: 767px) {
+  .sidebar { display: none; }
+  .mobile-header { display: flex; }
+  .app-body {
+    display: flex;
+    flex-direction: column;
+    flex: 1;
+  }
+}
+
+/* ── Sidebar components ────────────────────────────────────────────────── */
+.sidebar-brand {
+  padding: 0 1rem 1rem;
+  font-size: 13px;
+  font-weight: 600;
+  letter-spacing: 0.02em;
+}
+
+.sidebar-brand a {
+  text-decoration: none;
+  color: var(--fg);
+}
+
+.sidebar-nav {
+  display: flex;
+  flex-direction: column;
+  flex: 1;
+  gap: 0.125rem;
+  padding: 0 0.5rem;
+}
+
+.nav-link {
+  padding: 0.5rem 0.75rem;
+  border-radius: var(--radius);
+  color: var(--fg);
+  text-decoration: none;
+  font-size: 14px;
+  transition: background 0.1s ease;
+}
+
+.nav-link:hover,
+.nav-link:focus-visible {
+  background: var(--bg-elevated);
+  outline: none;
+}
+
+.nav-link.nav-active {
+  font-weight: 600;
+  background: var(--bg-elevated);
+  color: var(--fg);
+}
+
+.sidebar-footer {
+  padding: 1rem;
+  display: flex;
+  flex-direction: column;
+  gap: 0.25rem;
+  border-top: 1px solid var(--border-color);
+  margin-top: auto;
+}
+
+.sidebar-user {
+  font-size: 11px;
+  color: var(--fg-muted);
+}