feat(site-builder): selection breadcrumb, Esc selects parent, Tab cycles siblings

Refs #34

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

craft/src/styles/editor.css

@@ -2232,3 +2232,44 @@ body {
   color: var(--color-text-muted);
   text-align: center;
 }
+
+/* #34 breadcrumb */
+.canvas-breadcrumb {
+  display: flex;
+  align-items: center;
+  gap: 2px;
+  flex: 0 0 28px;
+  height: 28px;
+  padding: 0 10px;
+  overflow-x: auto;
+  white-space: nowrap;
+  background: var(--color-bg-surface);
+  border-bottom: 1px solid var(--color-border);
+  font-size: 12px;
+}
+
+.canvas-breadcrumb-sep {
+  color: var(--color-text-dim);
+  user-select: none;
+}
+
+.canvas-breadcrumb-crumb {
+  padding: 2px 6px;
+  font: inherit;
+  color: var(--color-text-muted);
+  background: transparent;
+  border: 0;
+  border-radius: var(--radius-sm);
+  cursor: pointer;
+}
+
+.canvas-breadcrumb-crumb:hover {
+  color: var(--color-text);
+  background: var(--color-bg-hover);
+}
+
+.canvas-breadcrumb-crumb[aria-current='true'] {
+  color: var(--color-text);
+  background: var(--color-accent-subtle);
+  cursor: default;
+}