feat(topbar): change environment prop from string to ReactNode

Allows consuming apps to pass a custom dropdown or any interactive
element instead of a static string label. Rendering changed from
<span> to <div> to support block-level children.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

COMPONENT_GUIDE.md

@@ -306,7 +306,7 @@ import {
 | Sidebar | Composable compound sidebar shell with icon-rail collapse mode. Sub-components: `Sidebar.Header`, `Sidebar.Section`, `Sidebar.Footer`, `Sidebar.FooterLink`. The app controls all content via children — the DS provides the frame. |
 | SidebarTree | Data-driven tree for sidebar sections. Accepts `nodes: SidebarTreeNode[]` with expand/collapse, starring, keyboard nav, search filter, and path-based selection highlighting. |
 | useStarred | Hook for localStorage-backed starred item IDs. Returns `{ starredIds, isStarred, toggleStar }`. |
-| TopBar | Header bar with breadcrumb, search trigger, ButtonGroup status filters, time range selector, theme toggle, environment badge, user avatar |
+| TopBar | Header bar with breadcrumb, search trigger, ButtonGroup status filters, time range selector, theme toggle, environment slot (`ReactNode` — pass a string for a static label or a custom dropdown for interactive selection), user avatar |
 
 ## Import Paths