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).

__tests__/MessageBubble.test.tsx

@@ -0,0 +1,154 @@
+import { act, fireEvent, render, screen } from '@testing-library/react-native';
+import * as Clipboard from 'expo-clipboard';
+import React from 'react';
+import { MessageBubble } from '../components/chat/MessageBubble';
+import { ChatMessage } from '../store/useAppStore';
+
+jest.mock('expo-clipboard', () => ({ setStringAsync: jest.fn(() => Promise.resolve(true)) }));
+
+let actionsProps: any;
+jest.mock('../components/chat/MessageActions', () => ({
+    MessageActions: (props: any) => {
+        actionsProps = props;
+        const { Text } = require('react-native');
+        return <Text>actions</Text>;
+    },
+}));
+
+const message = (overrides: Partial<ChatMessage> = {}): ChatMessage => ({
+    id: '1',
+    role: 'assistant',
+    content: 'hello **world**',
+    timestamp: new Date(2026, 0, 1, 13, 5).getTime(),
+    ...overrides,
+});
+
+beforeEach(() => {
+    actionsProps = undefined;
+    (Clipboard.setStringAsync as jest.Mock).mockClear();
+});
+
+describe('MessageBubble user message', () => {
+    it('shows the plain text and keeps the actions hidden until touched', () => {
+        render(<MessageBubble message={message({ role: 'user', content: 'hi there' })} />);
+        expect(screen.getByText('hi there')).toBeTruthy();
+        expect(screen.queryByText('actions')).toBeNull();
+    });
+
+    it('reveals edit and delete (but not regenerate) after a touch', () => {
+        const onEdit = jest.fn();
+        const onDelete = jest.fn();
+        const onRegenerate = jest.fn();
+        render(
+            <MessageBubble
+                message={message({ role: 'user', content: 'hi' })}
+                onEdit={onEdit}
+                onDelete={onDelete}
+                onRegenerate={onRegenerate}
+                isLastAssistant
+            />,
+        );
+        fireEvent(screen.getByText('hi').parent!.parent!.parent!.parent!, 'touchStart');
+
+        expect(screen.getByText('actions')).toBeTruthy();
+        expect(actionsProps.role).toBe('user');
+        expect(actionsProps.onEdit).toBe(onEdit);
+        expect(actionsProps.onDelete).toBe(onDelete);
+        expect(actionsProps.onRegenerate).toBeUndefined();
+    });
+
+    it('never renders actions for an empty message', () => {
+        render(<MessageBubble message={message({ role: 'user', content: '' })} />);
+        fireEvent(screen.getByText(/\d/).parent!.parent!.parent!, 'touchStart');
+        expect(screen.queryByText('actions')).toBeNull();
+    });
+});
+
+describe('MessageBubble assistant message', () => {
+    it('renders markdown and always shows actions', () => {
+        render(<MessageBubble message={message()} />);
+        expect(screen.getByText('world')).toBeTruthy();
+        expect(screen.getByText('actions')).toBeTruthy();
+    });
+
+    it('offers regenerate only on the last assistant message and never edit', () => {
+        const onEdit = jest.fn();
+        const onRegenerate = jest.fn();
+        const { rerender } = render(<MessageBubble message={message()} onEdit={onEdit} onRegenerate={onRegenerate} />);
+        expect(actionsProps.onRegenerate).toBeUndefined();
+        expect(actionsProps.onEdit).toBeUndefined();
+
+        rerender(<MessageBubble message={message()} onEdit={onEdit} onRegenerate={onRegenerate} isLastAssistant />);
+        expect(actionsProps.onRegenerate).toBe(onRegenerate);
+        expect(actionsProps.onEdit).toBeUndefined();
+    });
+
+    it('flags actions as streaming only for the last assistant message', () => {
+        const { rerender } = render(<MessageBubble message={message()} isStreaming />);
+        expect(actionsProps.isStreaming).toBeFalsy();
+
+        rerender(<MessageBubble message={message()} isStreaming isLastAssistant />);
+        expect(actionsProps.isStreaming).toBe(true);
+    });
+
+    it('renders nothing inside the bubble or actions while an empty answer is streaming', () => {
+        render(<MessageBubble message={message({ content: '' })} isStreaming isLastAssistant />);
+        expect(screen.queryByText('actions')).toBeNull();
+    });
+
+    it('renders an empty answer as markdown when not streaming', () => {
+        render(<MessageBubble message={message({ content: '' })} />);
+        expect(screen.queryByText('actions')).toBeNull();
+    });
+});
+
+describe('MessageBubble metadata', () => {
+    it('shows the time and the edited badge only for edited messages', () => {
+        const { rerender } = render(<MessageBubble message={message({ role: 'user' })} />);
+        expect(screen.queryByText(/edited/)).toBeNull();
+
+        rerender(<MessageBubble message={message({ role: 'user', isEdited: true })} />);
+        expect(screen.getByText(/· edited/)).toBeTruthy();
+    });
+});
+
+describe('MessageBubble code blocks', () => {
+    const fenced = 'text\n\n```ts\nconst a = 1;\n```\n';
+
+    it('shows the language, the code and copies it to the clipboard', async () => {
+        jest.useFakeTimers();
+        try {
+            render(<MessageBubble message={message({ content: fenced })} />);
+            expect(screen.getByText('ts')).toBeTruthy();
+            expect(screen.getByText(/const a = 1;/)).toBeTruthy();
+            expect(screen.getByText('Copy')).toBeTruthy();
+
+            await act(async () => {
+                fireEvent.press(screen.getByText('Copy'));
+            });
+            expect(Clipboard.setStringAsync).toHaveBeenCalledWith('const a = 1;\n');
+            expect(screen.getByText('Copied!')).toBeTruthy();
+
+            act(() => {
+                jest.advanceTimersByTime(2000);
+            });
+            expect(screen.getByText('Copy')).toBeTruthy();
+        } finally {
+            jest.useRealTimers();
+        }
+    });
+
+    it('labels a fence without a language as "code"', () => {
+        render(<MessageBubble message={message({ content: '```\nplain\n```\n' })} />);
+        expect(screen.getByText('code')).toBeTruthy();
+    });
+
+    it('renders indented code blocks with a "code" header and copy button', async () => {
+        render(<MessageBubble message={message({ content: 'intro\n\n    indented()\n' })} />);
+        expect(screen.getByText('code')).toBeTruthy();
+        await act(async () => {
+            fireEvent.press(screen.getByText('Copy'));
+        });
+        expect(Clipboard.setStringAsync).toHaveBeenCalledWith(expect.stringContaining('indented()'));
+    });
+});