splash: scale the logo to the pane instead of dropping itHEADmain

Reported as "the splash logo stopped rendering". It had not stopped: the
splash asks for the artwork's NATURAL size and shows nothing when that
does not fit, and the artwork needs 31 rows plus 10 of box chrome. A pane
in a split zellij window is 31 rows — one row short of the 41 it wanted —
so the logo silently disappeared. Traced with $IDATUI_KITTY_LOG in the
real session:

    compose: supported=True app.size=Size(width=159, height=31)
             cells=60x23 fits=False

The terminal scales an image into whatever cell box it is placed in
(`c=`/`r=` on the placement), so there was never a reason for
all-or-nothing. `logo_cells(max_rows)` now fits the art to the room left
after the box's furniture, and the same number reserves the cells and
sizes the placement, so a resize needs no relayout. In that same 31-row
pane it now draws 55x21 instead of nothing.

Two things fixed on the way:

* The chrome constant was one row optimistic (`rows + 9` where the box
  measures 10: border 2, padding 2, art margin 1, title 1, note 1+1,
  help 1+1). At exactly the old threshold the help line was clipped off
  the bottom.
* `_fits` conflated "is the terminal big enough" with "is the artwork the
  right size", which is what made the image path inherit the block art's
  all-or-nothing behaviour. The block art genuinely cannot scale (it is
  half-block cells, 26 rows) and still falls back to the text splash;
  the image no longer does.

`splash_scaling` pins it at 31, 30 and 44 rows: the logo is drawn, it is
scaled to the room, the box is never clipped, and a big pane still gets
the natural size.

905 passed, 0 failed.

0 files changed, 0 insertions, 0 deletions