feat(home): replace demo with entity count dashboard

Home page now shows one clickable summary card per entity type
(Networks, Hosts, Applications). Each card displays the total count
fetched from the database via a single get_summary() server function,
then navigates to the corresponding page on click.

Counts are pre-rendered server-side via <Suspense> so the page is
useful even before the WASM bundle loads.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/api/mod.rs

@@ -17,3 +17,4 @@
 pub mod applications;
 pub mod hosts;
 pub mod networks;
+pub mod summary;