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/index.ts

@@ -9,6 +9,8 @@ export { useMessages } from './hooks/use-messages';
 export { useChannels } from './hooks/use-channels';
 export { useMembers } from './hooks/use-members';
 export { isOwnMessage } from './types';
+// Message-body markup (bold/italic/strike/code/links + mentions) as a safe ReactNode tree.
+export { renderRichText, safeHref } from './rich-text';
 
 // Rendered UI. Pair with the './styles.css' export (or override the --miu-* tokens).
 export { Messenger } from './components/messenger';