#### Brief overview of PR changes/additions
- "Copy as image" with nothing selected now copies the visible screen
(timestamps included) instead of doing nothing. With a selection it is
unchanged.
- Copy, Copy HTML and Search on ... genuinely need a selection, so
without one they are greyed out with a tooltip saying so rather than
silently doing nothing.
- Copy as image no longer wipes the clipboard when it runs out of its 3s
budget, crops the drawn lines instead of squashing the whole selection
to fit, and copies a run of blank lines rather than nothing.
#### Motivation for adding to Mudlet
Right-clicking the console and picking "Copy as image" left nothing on
the clipboard, with no hint that a selection was needed.
#### Other info (issues closed, discussion etc)
Fixes#9715
Also fixes two ways a selection could outlive the lines it covers:
clearing a console now clears its selection (`clearWindow()` then "Copy
as image" aborted on Qt's bounds assert), and a selection stranded by
the buffer hitting its size limit is followed down with its lines
instead of copying whatever took their place.
New `CopyAsImageTest` functional test, 15 cases. Verified on X11 with
`xclip -selection clipboard -t image/png -o`.
Assisted-by: Claude:claude-opus-5
**Test case:** Right-click the main console with nothing selected, pick
"Copy as image", and paste - you get a picture of the screen. Select
some text and repeat - you get just the selection.
