feat: add Sidebar onNavigate callback and DataTable fillHeight prop

Sidebar: add optional onNavigate prop so consuming apps can intercept
and remap navigation paths instead of relying on internal React Router
links.

DataTable: add fillHeight prop for flex-fill layouts with scrolling
body. Make the table header sticky by default so it stays visible
during vertical scroll.

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

src/design-system/layout/Sidebar/SidebarTree.tsx

@@ -34,6 +34,7 @@ export interface SidebarTreeProps {
   filterQuery?: string
   persistKey?: string     // sessionStorage key to persist expand state across remounts
   autoRevealPath?: string | null  // when set, auto-expand the parent of the matching node
+  onNavigate?: (path: string) => void
 }
 
 // ── Star icons ───────────────────────────────────────────────────────────────
@@ -134,8 +135,10 @@ export function SidebarTree({
   filterQuery,
   persistKey,
   autoRevealPath,
+  onNavigate,
 }: SidebarTreeProps) {
-  const navigate = useNavigate()
+  const routerNavigate = useNavigate()
+  const navigate = onNavigate ?? routerNavigate
 
   // Expand/collapse state — optionally persisted to sessionStorage
   const [userExpandedIds, setUserExpandedIds] = useState<Set<string>>(