Preserve formatting, hyperlinks, and emojis when pasting formatted text into chat

### User Problem

When I paste formatted text into the chat, the formatting is completely lost. This also affects text with embedded hyperlinks and emojis, where the visible link text, actual URL, or emoji context may no longer be preserved properly. This makes it hard to revise or adapt existing text with exxperts.

### Feature Request

Support pasted text formatting better so that common formatting, embedded hyperlinks, and emojis are preserved when I paste content into the chat.

**Example:**

- I copy formatted text from another source
- The text includes headings, lists, bold text, spacing, embedded hyperlinks, and emojis
- I paste it into the chat
- The formatting, hyperlinks, and emojis are preserved where possible
- I can directly adjust the text without manually recreating the formatting, adding links again, or restoring emojis

Start by locating the chat composer and its paste-handling entry point, then inspect how pasted content is currently converted before submission. Define completion against the examples in the issue: preserve common formatting, embedded link text and URLs, spacing, and emojis where possible, with coverage for each case in the relevant UI tests.

Written by the indexing model from the issue text.