sl0p: ignore gap/padding when a pane draws no frame

Closes the frameless-mode hole documented in the README.

In frameless mode (pane_frame_style "titles" or "none") the cells around a
pane's content are owned by the inter-pane boundary renderer, not the pane.
The ghost-fix commit correctly stopped panes from BLANKING that region -
blanking it erased the boundaries and broke three tests - but nothing stopped
them from CREATING it: padding still inset the content, so the vacated cells
had no owner and kept whatever was drawn there before.

Half the job done in each direction produced exactly the ghosting the blanking
was meant to prevent, just in a mode we do not use by default.

Fix: a pane that is not drawing a frame is not inset at all - no gap, no
padding, no moat, nothing unowned. Pane::set_frame() already received the
right boolean from both the tiled and floating containers and was throwing it
away; it now records it.

Config values are preserved, they simply take effect only with full frames.
README updated to describe this as a defined limit rather than a known bug.

Baselines held: zellij-server 1421/30, zellij-utils 435/5.

0 files changed, 0 insertions, 0 deletions