feat(messaging-ui): message formatting + native spellcheck in the composer

Composer becomes a <textarea> so the PLATFORM supplies text services: red
spellcheck squiggles, right-click suggestions / add-to-dictionary, and mobile
autocorrect (spellCheck + autoCorrect + autoCapitalize). Nothing shipped for it.
Previously a single-line <input>, which Firefox does not spellcheck by default
(layout.spellcheckDefault=1 checks multi-line only) and which could not hold a
multi-line message at all. Enter sends, Shift+Enter (and IME composition) makes a
newline, and the box grows with content.

WhatsApp-style markup: *bold*, _italic_, ~strike~, `code`, ```fenced blocks```,
plus bare URLs. Cmd/Ctrl+B/I/E and a small toolbar wrap the selection in markers.
Messages stay PLAIN TEXT on the wire, so stored history and older clients are
unaffected — formatting is purely a render concern.

renderRichText() returns a ReactNode tree and never uses dangerouslySetInnerHTML,
so message text cannot inject markup; links are restricted to http/https/mailto
(safeHref) to close the javascript: vector. Code is tokenized first and its
contents stay literal; markers require word boundaries so snake_case_name and
"5 * 3" are not mangled.

Bumped to 0.1.9. SDK suite: 17 files / 95 tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/iios-messaging-ui/src/components/message-item.tsx

@@ -1,5 +1,5 @@
 import { useRef, useState } from 'react';
-import { highlightMentions } from '../mentions';
+import { renderRichText } from '../rich-text';
 import { PopoverPortal } from './popover-portal';
 import type { Attachment } from '../types';
 import type { UiMessage } from '../hooks/use-messages';
@@ -65,7 +65,7 @@ export function MessageItem({
     <div className={`miu-msg${message.mine ? ' is-mine' : ''}${message.pending ? ' is-pending' : ''}`}>
       <div className="miu-bubble-row">
         <div className="miu-bubble">
-          {m.text ? highlightMentions(m.text, memberNames) : null}
+          {m.text ? renderRichText(m.text, memberNames) : null}
           {m.attachment ? <AttachmentView att={m.attachment} /> : null}
         </div>
         <time className="miu-msg-time" dateTime={m.at} title={Number.isNaN(+new Date(m.at)) ? '' : new Date(m.at).toLocaleString()}>