fix(ui): implement UI review findings — a11y, IA, and consistency fixes

Fixes the reviewed gaps: keyboard-inaccessible delete controls (SessionRail,
Entities row), case-sensitive entity filter, two competing entity-detail
navigation patterns (standardize on EntitySheet), non-clickable Overview KPI
cards, a bare button bypassing the shared Button component, inconsistent
blur-only vs live filtering, and an unenforced sanitization assumption on
search snippet HTML (now using the already-present dompurify dependency).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/pages/Graph.svelte

@@ -8,6 +8,7 @@
   import { Badge } from '$lib/components/ui/badge'
   import * as Sheet from '$lib/components/ui/sheet'
   import { Skeleton } from '$lib/components/ui/skeleton'
+  import EntitySheet from '$lib/components/EntitySheet.svelte'
   import LocateFixedIcon from '@lucide/svelte/icons/locate-fixed'
 
   interface Node extends Entity {
@@ -289,6 +290,14 @@
     search = ''
     load()
   }
+
+  let entitySheetOpen = $state(false)
+  let entitySheetSlug = $state<string | null>(null)
+
+  function openEntityDetail(slug: string) {
+    entitySheetSlug = slug
+    entitySheetOpen = true
+  }
 </script>
 
 <div class="flex h-full flex-col gap-3 p-4">
@@ -461,7 +470,7 @@
       </Sheet.Header>
       <div class="flex flex-col gap-4 overflow-y-auto px-4 pb-4">
         <div class="flex gap-2">
-          <Button variant="outline" size="sm" onclick={() => (location.hash = '#/entity/' + encodeURIComponent(selected!.slug))}>
+          <Button variant="outline" size="sm" onclick={() => openEntityDetail(selected!.slug)}>
             View entity detail
           </Button>
           <Button variant="outline" size="sm" onclick={() => rerootTo(selected as Node)}>Re-root here</Button>
@@ -504,3 +513,5 @@
     {/if}
   </Sheet.Content>
 </Sheet.Root>
+
+<EntitySheet slug={entitySheetSlug} bind:open={entitySheetOpen} />