feat(client): add ContextMenu component, environment cards, detail page, and breadcrumbs

- add ContextMenu component with click-outside/Escape dismiss, align prop, and danger variant
- replace EnvironmentsPage table with responsive card grid
- add cog button to each card opening a context menu with view and delete actions
- add EnvironmentDetailPage at /environments/:id with meta grid, URLs card, and delete
- add Breadcrumbs to all pages; detail page uses two-item trail with delete button inline
- add Table stories for pagination and Timestamp column

client/src/ui/ContextMenu/ContextMenu.module.css

@@ -0,0 +1,60 @@
+.root {
+  position: relative;
+  display: inline-flex;
+}
+
+.triggerWrap {
+  display: inline-flex;
+}
+
+.menu {
+  position: absolute;
+  top: calc(100% + var(--space-1));
+  z-index: 100;
+  min-width: 160px;
+  margin: 0;
+  padding: var(--space-1) 0;
+  list-style: none;
+  background: var(--color-bg-subtle);
+  border: var(--border-width) solid var(--color-border);
+  border-radius: var(--radius-md);
+  box-shadow: var(--shadow-md);
+}
+
+.alignRight { right: 0; }
+.alignLeft  { left: 0; }
+
+.item {
+  display: flex;
+  align-items: center;
+  gap: var(--space-2);
+  width: 100%;
+  padding: var(--space-2) var(--space-4);
+  background: transparent;
+  border: none;
+  text-align: left;
+  font-family: var(--font-family);
+  font-size: var(--font-size-sm);
+  color: var(--color-text);
+  cursor: pointer;
+  transition: background var(--transition), color var(--transition);
+  white-space: nowrap;
+}
+
+.item:hover {
+  background: var(--color-secondary);
+}
+
+.item.danger {
+  color: var(--color-danger);
+}
+
+.item.danger:hover {
+  background: var(--color-error-bg);
+}
+
+.icon {
+  display: inline-flex;
+  align-items: center;
+  opacity: 0.75;
+}