feat(room-settings): one-line "who can see this" under the room name (#133)

Room Settings → General now reads e.g. "Encrypted · Invite only ·
History visible to members since they joined" under the name — derived
from m.room.encryption, m.room.join_rules and m.room.history_visibility
with the same words the preview-card chips and the history setting use.
One Text line, no card, no icons, no controls; spec defaults (invite-only,
shared history) when a state event is absent. Unit-tested.

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

src/app/utils/roomVisibilityLine.test.ts

@@ -0,0 +1,27 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { describeRoomVisibility } from './roomVisibilityLine';
+
+test('describeRoomVisibility composes the three facts', () => {
+  assert.equal(
+    describeRoomVisibility({ encrypted: true, joinRule: 'invite', historyVisibility: 'joined' }),
+    'Encrypted · Invite only · History visible to members since they joined',
+  );
+  assert.equal(
+    describeRoomVisibility({ encrypted: false, joinRule: 'public', historyVisibility: 'shared' }),
+    'Not encrypted · Anyone can join · History visible to members, including before they joined',
+  );
+  assert.equal(
+    describeRoomVisibility({
+      encrypted: false,
+      joinRule: 'knock',
+      historyVisibility: 'world_readable',
+    }),
+    'Not encrypted · Ask to join · History visible to anyone, even guests',
+  );
+  // Missing state: spec defaults are invite-only and "shared".
+  assert.equal(
+    describeRoomVisibility({ encrypted: true }),
+    'Encrypted · Invite only · History visible to members, including before they joined',
+  );
+});

src/app/utils/roomVisibilityLine.ts

@@ -0,0 +1,49 @@
+import { HistoryVisibility, JoinRule } from 'matrix-js-sdk';
+
+/**
+ * [Gitea #133] One sentence for Room Settings → General, under the name:
+ * "Encrypted · Invite only · History visible to members since they joined".
+ * Wording mirrors the room preview card chips and the history-visibility
+ * setting so the same words mean the same thing everywhere.
+ */
+export function describeRoomVisibility(input: {
+  encrypted: boolean;
+  joinRule?: string;
+  historyVisibility?: string;
+}): string {
+  const parts: string[] = [input.encrypted ? 'Encrypted' : 'Not encrypted'];
+  switch (input.joinRule) {
+    case JoinRule.Public:
+      parts.push('Anyone can join');
+      break;
+    case JoinRule.Knock:
+    case 'knock_restricted':
+      parts.push('Ask to join');
+      break;
+    case JoinRule.Restricted:
+      parts.push('Restricted');
+      break;
+    case JoinRule.Private:
+      parts.push('Private');
+      break;
+    case JoinRule.Invite:
+    default:
+      parts.push('Invite only');
+  }
+  switch (input.historyVisibility) {
+    case HistoryVisibility.WorldReadable:
+      parts.push('History visible to anyone, even guests');
+      break;
+    case HistoryVisibility.Invited:
+      parts.push('History visible to members since they were invited');
+      break;
+    case HistoryVisibility.Joined:
+      parts.push('History visible to members since they joined');
+      break;
+    case HistoryVisibility.Shared:
+    default:
+      // "shared" is also the spec default when the state event is absent.
+      parts.push('History visible to members, including before they joined');
+  }
+  return parts.join(' · ');
+}