fix(web): SearchInput passes keepFocus to goto() to prevent blur on debounce

The actual cause of the search-field focus loss: SvelteKit's `goto()`
defaults to resetting focus on navigation, so each debounced URL update
blurred the input mid-typing. Pass `keepFocus: true` to both `goto()`
calls in `navigate()`.

The earlier `bind:value` change in 6931358 didn't address this — it was
solving a hypothetical DOM-write-side cursor-jump issue rather than the
real focus-reset behavior. Leaving `bind:value` in place since it's
still cleaner Svelte 5.

Tests updated to match the new goto args.

web/src/lib/components/SearchInput.svelte

@@ -17,11 +17,17 @@
   function navigate(next: string) {
     const onSearchPage = page.url.pathname.startsWith('/search');
     const trimmed = next.trim();
+    // keepFocus: SvelteKit blurs the active element on navigation by default.
+    // For a typeahead-style URL update we want the user to keep typing
+    // without re-clicking the input every 250 ms.
     if (trimmed === '') {
-      if (onSearchPage) goto('/search', { replaceState: true });
+      if (onSearchPage) goto('/search', { replaceState: true, keepFocus: true });
       return;
     }
-    goto(`/search?q=${encodeURIComponent(trimmed)}`, { replaceState: onSearchPage });
+    goto(`/search?q=${encodeURIComponent(trimmed)}`, {
+      replaceState: onSearchPage,
+      keepFocus: true,
+    });
   }
 
   function onInput() {