feat(calls): undeafen catch-up toast (#128)

On deafen the participant set is snapshotted; on undeafen it is diffed and,
only if it changed and you were deafened for at least 10 s, one auto-dismissing
toast says 'While you were deafened: Alice, Bob joined · Cole left' (names
capped at 3 + N more). Rides the membership stream that already drives the
join/leave sounds — no new subscriptions; PTT holds don't touch deafen so they
can't trigger it. Verified headless: short deafen → nothing; bob leaves during
an 11 s deafen → 'bob left'; long deafen with no change → nothing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/utils/deafenCatchUp.test.ts

@@ -0,0 +1,17 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { deafenCatchUpText } from './deafenCatchUp';
+
+const name = (u: string) => u.slice(1, u.indexOf(':'));
+
+test('no change → nothing; joins and leaves are listed, capped at 3 + N more', () => {
+  assert.equal(deafenCatchUpText(new Set(['@a:x']), new Set(['@a:x']), name), null);
+  assert.equal(
+    deafenCatchUpText(new Set(['@a:x', '@c:x']), new Set(['@a:x', '@b:x']), name),
+    'While you were deafened: b joined · c left',
+  );
+  assert.equal(
+    deafenCatchUpText(new Set(), new Set(['@a:x', '@b:x', '@c:x', '@d:x', '@e:x']), name),
+    'While you were deafened: a, b, c and 2 more joined',
+  );
+});

src/app/utils/deafenCatchUp.ts

@@ -0,0 +1,27 @@
+/**
+ * [Gitea #128] "While you were deafened: Alice, Bob joined · Cole left".
+ * Pure diff + wording; the hook snapshots the participant set on deafen and
+ * calls this on undeafen.
+ */
+export const DEAFEN_CATCHUP_MIN_MS = 10_000;
+const MAX_NAMES = 3;
+
+const list = (names: string[]): string => {
+  const shown = names.slice(0, MAX_NAMES);
+  const more = names.length - shown.length;
+  return more > 0 ? `${shown.join(', ')} and ${more} more` : shown.join(', ');
+};
+
+export const deafenCatchUpText = (
+  before: Set<string>,
+  after: Set<string>,
+  nameOf: (userId: string) => string,
+): string | null => {
+  const joined = Array.from(after).filter((u) => !before.has(u));
+  const left = Array.from(before).filter((u) => !after.has(u));
+  if (joined.length === 0 && left.length === 0) return null;
+  const parts: string[] = [];
+  if (joined.length) parts.push(`${list(joined.map(nameOf))} joined`);
+  if (left.length) parts.push(`${list(left.map(nameOf))} left`);
+  return `While you were deafened: ${parts.join(' · ')}`;
+};