[Enhancement] Markdown rendering in chat bubbles

[8dazo]

Description

Agent responses are currently plain text. Render markdown formatting to improve readability.

Implementation

• Integrate a React Native markdown renderer (e.g., react-native-markdown-display)
• Support bold, italics, code blocks, lists, and links

Acceptance Criteria

• Agent responses show rich text
• Code blocks have distinct styling
• Links are clickable