Improve verification and media UX

[mjkatgithub]

Goal

Improve the end-to-end encryption (E2EE) user experience so that verification
state is clear and media handling is predictable.

This is based on real user feedback:

• Session verification appears inconsistent vs Element.
• Emoji comparison UI is not shown (or does nothing).
• Image uploads/messages may not render until switching rooms.
• Decryption failures show a raw error message.

Scope

• Verification UX
  • Ensure Decentra’s verification state matches the underlying crypto state.
  • Provide a clear UI entry point to verify the current session/device.
  • When verification is required, show an explicit prompt and a working flow.
  • Add an Element-like hint/badge for content coming from an unverified session
    (at minimum for images/attachments; ideally also for encrypted messages).
• Media rendering reliability
  • Fix image/attachment events not appearing immediately after send/receive.
  • Ensure media thumbnails/previews update without requiring a room switch.
• Error messaging
  • Replace “encrypted message could not be decrypted” style raw errors with a
    user-friendly state + action hints (e.g. retry, wait for keys, verify).

Acceptance Criteria

• Verification status shown in UI is consistent with actual crypto state.
• Emoji/SAS compare flow is accessible and functional when verification is
  possible.
• Images/attachments render immediately after they are sent/received (no
  manual room switch required).
• If a message/media is from an unverified session, Decentra shows a clear
  non-blocking warning similar to Element (e.g. “Session not verified”).
• Decryption failures are presented as a friendly UI state and do not show
  raw technical strings to end users.

Test Checklist

Unit

• Verification state mapping (verified/unverified/unknown) -> UI model
• Media event -> timeline render update (reactivity)
• Decryption error mapping -> user-friendly message

Integration

• Verify session flow triggers expected crypto calls and UI transitions
• Send image and observe immediate render without navigation
• Receive image and observe immediate render without navigation

E2E

• Login with a new session, trigger verification, complete SAS compare
• Send/receive an image in an encrypted room and verify it displays
• Simulate a decrypt failure and verify the friendly error UI

Notes

• Element displays media with a hint about the unverified session; Decentra
  should implement a comparable hint/badge.

Branch

feature/verification-media-ux