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/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@insignia/iios-messaging-ui",
-  "version": "0.1.8",
+  "version": "0.1.9",
   "type": "module",
   "main": "dist/index.js",
   "module": "dist/index.js",