## Why
`Ctrl+V` previously attempted only image paste, so a text-only clipboard produced an image-paste error. `Shift+Insert` did not use the clipboard paste path.
## What changed
- On Windows, let `Ctrl+V` and `Shift+Insert` paste images first, then read clipboard text asynchronously when no image is available. Keep clipboard access errors distinct from missing images.
- Allow keyboard paste into composer selections and active history or Vim search queries, including inline mode with right-click paste disabled.
- Flush buffered typing before explicit paste to preserve input order. Discard pending clipboard text when the thread or editable target changes, while allowing shortcut releases and repeated paste shortcuts to leave the read pending.
## Testing
Extend shortcut and clipboard-worker tests to cover text fallback, multiline Unicode text, stale-read cancellation, shortcut releases and repeats, and read-only drafts. Add assertions for history-search preview stability and selection changes.
GitOrigin-RevId: 080c1c05a4587e325cea938a6e28c646b9ac5837