feature: forward message lacks loading feedback when send is clicked

When forwarding a message, clicking the Send button provides minimal visual feedback (the button only changes to light grey). This makes it unclear whether the forwarding process has started. Additionally, users can continue selecting more channels even though the forwarding operation may already be in progress, leading to confusion about the current state.

Steps to Reproduce

1. Open a message you want to forward
2. Tap on the Forward option
3. Select one or more channels/recipients in the Person or channel field
4. Click the Send button
5. Observe the minimal visual feedback (button turns light grey only)

Expected Behavior

After clicking the Send button:

• A clear visual indicator should appear showing that forwarding is in progress
  • Preferably a Rocket.Chat loader or spinner
• The Send button should be disabled or show a loading state to prevent multiple submissions
• The channel selection field should be disabled while forwarding is in progress
• Users should clearly understand that the operation has started

Actual Behavior

• The Send button only changes to a light grey color
• No loading indicator or spinner is shown
• Users cannot tell if forwarding has started
• Users can continue adding more channels while forwarding is potentially in progress

Attachments

Forward dialog initial state	Send button disabled state	Channels selectable during forwarding

Start by locating the React Native forward dialog and the handler used by the Send button. Reproduce the forwarding flow with one or more channels, then inspect the existing disabled state and channel selector behavior. Done means forwarding visibly shows a loading state, prevents repeated submission, and disables channel selection until the operation finishes.