app.clipboard.pasteImage dead-ended with a status message when the
clipboard held text, which made the chord useless on hosts that only
deliver that one keypress (VS Code's integrated terminal forwarding
Ctrl+V, Windows clipboard history via Win+V simulating Ctrl+V).
- handleImagePaste now pastes clipboard text through the editor's
paste semantics when no image is available; an empty clipboard
reports 'Clipboard is empty'.
- readTextFromClipboard reaches the Windows clipboard through host
PowerShell under WSL (mirroring readImageFromClipboard), with CRLF
normalization and UTF-8 output encoding.
- handleClipboardTextRawPaste's empty-clipboard status message moved
to the actual empty branch (was shown after successful pastes).
- Clipboard reads are constructor-injectable for tests.
Implements proposal 1 of #1628.