[Web] Warn user before navigating when composer is open

[axiand]

Describe the bug
When the post composer is open, it's easy to lose a draft by accidentally refreshing or navigating in history.

To Reproduce

Steps to reproduce the behavior:

1. Open the post composer
2. Write some text
3. Hit the refresh button or back/forwards buttons
4. Post draft is lost

Expected behavior
I should be presented with a dialog like screenshot 1. that warns me before navigation occurs.

Screenshots

1. The browser dialog
   

Details

• Platform: Firefox, Windows 10
• Platform version: 130.0
• App version: Build version: 1.91.1; Bundle info: fb71fff (prod); Bundle date: 24091621; Platform: web

Additional context

(none)

[Nayelianne]

The amount of times I accidentally clicked away from the text box when editing my bio or a list description, and lost everything I've written because it just closed the window without warning... T_T