refactor(chat): split MessageBubble into avatar, content and code block components

MessageBubble CC 19 -> below 10. The fence and indented code block rules were identical and are now one CodeBlock component; the Markdown style map lives in markdownStyles.ts. Adds characterization tests for the bubble (roles, actions visibility, edited badge, copy feedback).

jest.config.js

@@ -4,6 +4,10 @@ module.exports = {
   moduleNameMapper: {
     '^@/(.*)$': '<rootDir>/$1',
   },
+  // jest-expo's default pattern plus the ESM-only markdown renderer.
+  transformIgnorePatterns: [
+    'node_modules/(?!((jest-)?react-native|@react-native(-community)?)|expo(nent)?|@expo(nent)?/.*|@expo-google-fonts/.*|react-navigation|@react-navigation/.*|@sentry/react-native|native-base|react-native-svg|@ronradtke/.*)',
+  ],
   testMatch: ['<rootDir>/__tests__/**/*.test.{ts,tsx}'],
   testPathIgnorePatterns: ['/node_modules/', '/dist/', '/.agent/'],
 };