v0.3.1

Added

• tests/pixels.rs: the pixel path, end to end. Eight tests over the half of
  the program that was not merely unasserted but unreachable. mossaic decides
  whether to draw pixels by asking the terminal, so a harness that answered no to
  every question could only be driven down the text path — the suite worked around
  that with --graphics sixel --cell 10x20, which forces the protocol and hands
  over the cell size, skipping the probe, the fallbacks and the auto choice.
  termlens 0.5 states which terminal is being simulated, so the real decision runs.

  What that buys, beyond the probe itself: the byte budgets in docs/DESIGN.md §4
  are now checked against the wire (a year is ~5 KB over kitty against ~44 KB of
  sixel, and the test holds the order of magnitude the design decision rests on);
  the diffing in §5 is checked the same way, since one cursor move costs under a
  tenth of a year rather than re-sending it; the cell contract in §3 is asserted
  through a terminal for the first time, with all seven grid rows left to the
  painter while the month labels stay text; --graphics text is checked to send no
  image at all on a terminal that could draw one; Auto is checked never to place
  an image too wide to fit; and --capabilities, which had no test at all because
  no harness could answer the questions it asks, is checked to agree with what the
  chart then does.

• Two tests for behaviour no content assertion can see. An idle chart repaints
  on an 80 ms timer so the loading spinner can turn, and every one of those frames
  shows exactly the right content — printable_chars is what shows that a settled
  chart writes nothing at all. And mossaic ignores keys it does not bind silently,
  which used to be the same screen as refusing them with a bell; bells() tells
  the two apart.

Changed

• termlens 0.4.2 → 0.5.0 (dev-dependency). send, send_str and paste
  return Result rather than panicking, so every input call in the suite now
  propagates with ? — 24 call sites, which is the whole migration.