fix(status): banner Details strips Markdown syntax, not every #, _, >, * (#308)

plain() deleted those characters everywhere, so "join #lotus-general"
lost its #, snake_case and @some_user lost underscores, "->" became
"-", "5 * 3" became "5  3", and "<b>" became "<b". Strip only syntax:
heading / quote / list markers at line start, paired **x** *x* _x_ `x`,
and HTML tags.

Fixes #308

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/utils/kumaStatus.test.ts

@@ -1,6 +1,7 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import {
+  plain,
   DEFAULT_GROUPS,
   kumaBeatTime,
   kumaUrls,
@@ -260,3 +261,27 @@ test('a dismissed calls-down banner lets the next one through, never hides serve
     'server-down',
   );
 });
+
+test('plain: strips Markdown syntax only, keeps ordinary #, _, > and * (#308)', () => {
+  assert.equal(
+    plain('join #lotus-general or #announcements:lotusguild.org'),
+    'join #lotus-general or #announcements:lotusguild.org',
+  );
+  assert.equal(
+    plain('ping @some_user about snake_case and C#'),
+    'ping @some_user about snake_case and C#',
+  );
+  assert.equal(
+    plain('calls -> fixed, > 5 people, 5 * 3 = 15'),
+    'calls -> fixed, > 5 people, 5 * 3 = 15',
+  );
+  assert.equal(
+    plain('# Heading\n* item one\n- item two\n> quoted'),
+    'Heading\nitem one\nitem two\nquoted',
+  );
+  assert.equal(plain('**bold**, *em*, _em_, `/sfu/get`'), 'bold, em, em, /sfu/get');
+  assert.equal(
+    plain('Read the <b>guide</b> <img src=x onerror=alert(1)> [docs](https://x.y)'),
+    'Read the guide  docs',
+  );
+});