feat(v1.1.1-dead-letters): dashboard badge + list view

Design notes §4 makes the dashboard surface load-bearing — with no
default DL handler, users wouldn't know dead letters exist
otherwise.

New route: `apps/[slug]/dead-letters/+page.svelte` — list view
columns per the design notes:
- `created_at`, `source`, `op`, `script_id`, `attempt_count`,
  `first/last_attempt_at`, `last_error` (truncated; clickable)
- per-row Replay + Mark resolved buttons
- expandable row detail panel showing full payload (JSON) +
  full last_error
- unresolved-only filter (default on); refresh button

Per-app detail page (`apps/[slug]/+page.svelte`) grows a "Dead
letters" link in the tabs nav, with a red unresolved-count pill
when > 0. Loaded in parallel with the existing app loaders so it
doesn't slow the page.

Apps list (`apps/+page.svelte`) shows the same red pill next to
each app's name when its unresolved count > 0. Counts fetched in
parallel after the apps list lands; failures here are non-fatal
(just no badge).

API client wiring: `api.deadLetters.{count,list,get,replay,resolve}`
mirrors the v1.1.1 admin endpoints. `DeadLetterRow` type added to
the dashboard's API shape declarations.

dashboard's svelte-check passes (369 files, 0 errors, 0 warnings).

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

dashboard/src/routes/apps/+page.svelte

@@ -12,6 +12,26 @@
 	let listError = $state<string | null>(null);
 	let loading = $state(true);
 
+	/// Unresolved-dead-letter count per app (v1.1.1). Loaded in
+	/// parallel after the app list. Failures here are non-fatal —
+	/// missing counts just don't render a badge.
+	let unresolvedDl = $state<Record<string, number>>({});
+	async function loadDlCounts(appList: App[]) {
+		const results = await Promise.all(
+			appList.map(async (a) => {
+				try {
+					const r = await api.deadLetters.count(a.id);
+					return [a.id, r.unresolved] as const;
+				} catch {
+					return [a.id, 0] as const;
+				}
+			})
+		);
+		const next: Record<string, number> = {};
+		for (const [id, count] of results) next[id] = count;
+		unresolvedDl = next;
+	}
+
 	let showCreate = $state(false);
 	let createSlug = $state('');
 	let createName = $state('');
@@ -49,6 +69,9 @@
 		listError = null;
 		try {
 			apps = await api.apps.list();
+			if (apps && apps.length > 0) {
+				void loadDlCounts(apps);
+			}
 		} catch (e) {
 			listError = e instanceof Error ? e.message : String(e);
 			apps = null;
@@ -201,6 +224,12 @@
 						<div class="primary">
 							<strong>{app.name}</strong>
 							<span class="muted">/{app.slug}</span>
+							{#if unresolvedDl[app.id] > 0}
+								<span
+									class="dl-badge"
+									title="Unresolved dead letters in this app"
+								>{unresolvedDl[app.id]}</span>
+							{/if}
 						</div>
 						<div class="secondary muted">
 							{app.description ?? '—'}
@@ -246,6 +275,19 @@
 		cursor: not-allowed;
 	}
 
+	.dl-badge {
+		display: inline-block;
+		min-width: 1.25rem;
+		padding: 0.1rem 0.4rem;
+		background: #ef4444;
+		color: #fff;
+		border-radius: 999px;
+		font-size: 0.75rem;
+		font-weight: 600;
+		text-align: center;
+		margin-left: 0.5rem;
+	}
+
 	.muted {
 		color: #64748b;
 	}