* fix(layout): add mobile sidebar trigger for small screens
The sidebar already renders as a Sheet (drawer) on mobile via the
existing shadcn sidebar component, but there was no trigger button
for users to open it. This adds a mobile-only (md:hidden) header
bar with a SidebarTrigger in the DashboardLayout so users on phones
can access the sidebar navigation.
Closes#593
* feat(views): add mobile-responsive layout for inbox page
On mobile (<768px), switch from resizable two-panel layout to a
full-screen list/detail toggle. Tapping a notification shows the
detail view full-screen with a back button; the sidebar trigger
from the dashboard layout remains accessible.