Full-width rail targets; drop the idle pill and the edited marker

[gbradham]

Three fixes from using the app, all reported together.

Rail entries are the full width of the rail

A QToolButton sizes itself to its label, so every entry on the Experiment
rail was a different width — Metadata 111px, Mice 85px, Zones 92px — and most
of the rail looked clickable while being inert. Reported as "they are
inconsistent and I find myself missing them", which is exactly what a target
that stops with the word produces.

— edited is gone from beside the experiment name

A strip that appends it the moment you type in the name is telling you what you
just did.

It was also the shell's only unsaved-work indicator — the tests said so in
a comment — so removing the text without replacing the signal would have left
none at all. setWindowModified takes it over: the dot in the close button on
macOS, an asterisk elsewhere, and the platform's own convention rather than an
invention of ours. Set on the window rather than the strip, so it also works
in runner mode, where there is no strip to carry it.

The run-state pill is hidden while idle

Idle is the state GLIDER is in almost all of the time, and an indicator that is
always on screen stops being read — which is the one failure this pill cannot
afford, since its whole job is to be noticed when a run starts or a board drops
out of one at 3am. Everything that is not idle appears exactly as before.

The pill and the dirty label are kept as widgets rather than deleted: both are
still driven by callers carrying real information, and the pill has to come
back the instant the state stops being idle.

Notes for review

• Tests were repointed, not relaxed. The claims they made are still true,
  they just live somewhere else — isWindowModified() instead of
  dirty_label().isVisible(). The toggle-placement test additionally had to
  start ignoring hidden widgets: a hidden one has no position, so its collapsed
  span would have failed that test for a reason unrelated to where the toggles
  sit.
• Docs updated with the code. The strip's contents table, its "what it
  carries" list, and the pill's own section all described what was just
  removed.
• If you'd rather the pill were gone outright, say so — hiding it only while
  idle was my reading of "the Idle can go", chosen because the strip is
  documented as the thing that must stay visible during an unattended run.

Testing

QT_QPA_PLATFORM=offscreen uv run --no-sync pytest -q -m "not slow" —
5124 passed, 3 skipped. ruff clean. Checked on screen: rail targets uniform
and full width, no pill, no — edited.