web(review): expandable Review group in sidebar, tabs become subitems

Mirrors the Tags affordance: chevron-only toggle, no /review landing
entry, navigation only via subitems (cause buckets + Stacks +
Cross-folder linked as /review?tab=<id>). Cause list reuses the
review-groups query so empty buckets stay hidden. The /review toolbar
drops the pill row and shows the active tab as a breadcrumb segment.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/routes/review/+page.svelte

@@ -15,7 +15,6 @@
 	approve). The previous section is restored on unmount.
 -->
 <script lang="ts">
-	import { goto } from '$app/navigation';
 	import { page } from '$app/state';
 	import { createQuery } from '@tanstack/svelte-query';
 	import {
@@ -138,49 +137,18 @@
 	});
 
 	const activeGroup = $derived(groups.find((g) => g.cause === activeTab));
-
-	function setTab(id: Tab) {
-		const params = new URLSearchParams();
-		// First cause tab (if any) is the default — same convention as
-		// the old /review behaviour, so back-from-cross-folder lands on
-		// the user's review queue rather than the empty Stacks panel.
-		const defaultId = tabs[0]?.id;
-		if (defaultId !== undefined && id !== defaultId) params.set('tab', id);
-		void goto(`/review${params.size ? '?' + params : ''}`, {
-			keepFocus: true,
-			noScroll: true
-		});
-	}
+	const activeTabSpec = $derived(tabs.find((t) => t.id === activeTab));
 </script>
 
 <Toolbar>
 	<span class="rounded-md border border-border px-2 py-0.5 text-[11px] text-muted-foreground">
 		Review
 	</span>
-	{#if tabs.length > 0}
-		<div class="flex items-center gap-1">
-			{#each tabs as t (t.id)}
-				<button
-					type="button"
-					class="inline-flex items-center gap-1 rounded border px-2 py-0.5 text-[11px] {activeTab === t.id
-						? 'border-primary/40 bg-primary/10 text-primary'
-						: 'border-border text-muted-foreground hover:bg-accent hover:text-foreground'}"
-					onclick={() => setTab(t.id)}
-				>
-					<span>{t.label}</span>
-					{#if t.count !== undefined}
-						<span
-							class="flex h-4 min-w-4.5 items-center justify-center rounded px-1 text-[10px] tabular-nums {activeTab ===
-							t.id
-								? 'bg-primary/15 text-primary'
-								: 'bg-secondary text-muted-foreground'}"
-						>
-							{t.count}
-						</span>
-					{/if}
-				</button>
-			{/each}
-		</div>
+	{#if activeTabSpec}
+		<span class="text-[11px] font-medium">{activeTabSpec.label}</span>
+		{#if activeTabSpec.count !== undefined}
+			<span class="text-[11px] text-muted-foreground">{activeTabSpec.count}</span>
+		{/if}
 	{/if}
 	{#snippet trailing()}
 		<div