Copy & share message

[mrsumanbiswas]

Add user‑friendly options to copy and share message content.

• Long‑press a message bubble → show a context menu with “Copy” and “Share”
• Copy: copy the text content to the device clipboard, show a subtle confirmation
• Share: use the OS share sheet to share the message text (and optionally an image of the message) to other apps

For future image messages, adapt sharing to share the media file. Keep the implementation simple for now.