feat(midiviz): a sun theme, a menu, and a tray it can hide into

PLN: "midimon unusable in the sun in light mode :') can we have a basic menu
for midimon, maybe a tray presence when runnig, with scaling, theme, etc
options ? to help sets in all context, robust, antifragile".

Colours leave the paint loop and become data: three themes resolved once per
change, so a frame still constructs no QColor and the 30/5 fps split is intact.
The cut that made it work is INK versus SURFACE — recency (digits, bars, pens)
against cell bodies, column glow and gutter — because the docstring's own
invariant is that a mapped-but-idle cell must never read as a hardware fault.
On dark that is a glow above black; on light and sun it is a wash below the
page. A test asserts the floor tint differs from the page on all three.

`sun` needed two passes and only a screenshot said so: the first render climbed
to a saturated mid-tone panel and the digits lost the fight against it — light
with fatter bars, not a sun theme. Flattened tint, near-black ink at every
decay level, and a bold face, which outdoors is the cheapest contrast there is.
The decayed state was shot on purpose, since "no subtle dim states" is exactly
about the moment after a movement ends.

Menu and tray are one QMenu, and every entry calls the same method the key
does — no second code path, and no setShortcut, which would have taken the keys
off keyPressEvent and out of the selftest's reach. Tray guarded on
isSystemTrayAvailable and silently absent otherwise; a hidden window drops to
idle fps and X/q/Quit still really exit.

Config at $XDG_CONFIG_HOME/parvagues/midiviz.json, temp-file plus os.replace,
and load cannot raise: missing, corrupt, not-a-dict, unknown-theme, NaN scale
and unwritable are each exercised. A monitor that dies on a bad config file is
worse than one with no config, and this one is meant for the middle of a set.

Verified: bridge tests 105 -> 121 passing (the single failure is the inherited
test_gearbox dash case, identical before and after); selftest PASS on all three
themes; and dark proven pixel-identical to HEAD at four scales by rendering
both versions side by side.

NOT verified, and not to be claimed: the tray on a real desktop. Headless has
no status area, so only the degrade path was proven. One known follow-up — a
window hidden to the tray is still alive, so the hub's focus_window does
nothing for it and the tray is the only recall path.