Create route structure with __root, index (redirect to /initiatives),
initiatives/index (dashboard stub), initiatives/$id (detail stub with
type-safe params), and inbox (stub). Add AppLayout with persistent nav
header matching wireframe: title, New Initiative button, navigation tabs
with active highlighting. Disabled tabs for Agents/Tasks/Settings (out
of scope). Replace temporary health-check App with RouterProvider.
Route tree auto-generated by TanStack Router Vite plugin.
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