feat: add media upload to DM conversations

[barrydeen]

Summary

• Add Blossom media upload support in DM conversations via an attach icon next to the text input
• Hide bottom navigation bar on the DM conversation screen for a cleaner chat experience
• Use reverse layout on the message list so messages stay pinned above the keyboard when it opens
• Add proper navigationBarsPadding to prevent the input from sitting behind the system nav bar

Test plan

• Open a DM conversation and tap the image icon to upload media
• Verify uploaded URL is inserted into the message text field
• Verify the bottom nav bar is hidden in DM conversations
• Verify the text input sits above the system navigation bar
• Open the keyboard and verify messages stay visible (not covered)
• Send a message with an attached media URL and verify it delivers