Slim the arp view, and move the controls onto the bars

[owenpkent]

Seven commits from one day of passes on the arp and the section bars. The
through-line: controls move out of bands that fold away and onto the bars
that survive the fold, and the window Keys opens in gets a lot shorter.

The arp

• The All view is two boxed line cards and nothing else. The twelve
  slots and the Copy / Clear / Stop / Chain row went back to the per-line
  tabs where every one of those buttons already is; LTCH, PLAY and Chain
  left the rows. Each card draws its own captioned frame (LINE A / LINE B)
  and the outer box is gone, because a frame around both was the strongest
  cue they were one thing. ~110 px off the window.
• A and B on the bar are power switches now, bound straight to
  arpOn / arp2On. They used to be a navigation tab with a separate On
  chip a few pixels away; the chip is deleted, and so is the macro card's
  own On toggle. An off line is scrimmed whole instead, with nothing on it
  disabled: a rate must be dialable before switching on, and a chord
  dropped onto an off line has to land. Details beside Anchor is the
  route from a card to that line's deep view.
• A click on a chord card never feeds a line. The drag - onto a card,
  a letter tab, or a slot - is the only way in. The one left-click arp
  behaviour kept is a stop.
• HUMAN split into H.TIME and H.VEL, and VOL became VEL: bipolar,
  centred on "as played", full left mutes. The multiplier is squared
  (hearing is logarithmic), multiplies after the engine's 0.05 audibility
  floor rather than before it, and bottoms at MIDI velocity 1.

The bars

• The tempo is a plain number on the Controls bar, Ableton-style:
  BpmField is a juce::Slider subclass that overrides paint, so the
  APVTS attachment still drives it while no LookAndFeel ever draws a track.
  The < > pair beside it is the click-only path the mouse-only contract
  wants - the one part of "just a number" Keys cannot copy from a DAW that
  expects a keyboard for that field.
• Root, Scale, Lock, Voices and MIDI Ch ride that bar too. They did not
  fit at the editor's floor, so the group has two sizes and measures
  which it can afford rather than assuming.
• Size and Octave move to the Keyboard bar, Humanize to the Pads bar,
  and the Knobs chip is deleted rather than hidden. The Controls band is
  one row now; headerH drops 112 -> 52.
• An Instrument chip gives KeysEditor its first extension point for
  something embedding it. Keys Host's own 44 px top bar is deleted with it.

Parameter layout changes - saved sessions

Three parameters appended per line (arpHumanVel*, arpVelTrim*) plus a
global bpmSync. Old sessions open sounding identical: Humanize carries on
as the timing half, migrateVelTrim folds Volume into VelTrim through the
same curve, and migrateBpmSync backfills the default.

Writing those migrations exposed a kit bug that had left every
absence-detecting migration silently dead (migrateStrumRange,
migrateRateMode included): state::load handed replaceState the parsed
root's own parameter child, and replaceState backfills absent parameters
into the shared tree before onExtra reads it. Fixed in
okstudio-juce-kit (StateHelpers.h); this PR pairs with that one.

The editor's minimum width moves to 1280, up from 1070.

Verification

Keys_tests: 166 cases, 2422 checks, all passing. Security review of the
branch found no HIGH or MEDIUM findings - the new drop target, the two
migrations and the velocity math all terminate in existing clamped choke
points.

[owenpkent]

Follow-up commit 0a5d817, both Owen's calls: the two lines are now side-by-side cards (rate/shape, eight knobs under their own headings, Dot/Trip/Anchor + held chord), and the VEL knob got three fixes for 'at -96 it was still pretty loud': squared response curve, the fader now applies after the engine's 0.05 audibility floor (bottoms at MIDI velocity 1 instead of pinning at 6 below about -90), and chords bound for a line's queue skip the keyboard Humanize velocity range so the 'as played' reference holds still. migrateVelTrim folds old Volumes through the curve, still level-exact. Tests updated and passing (162 cases).

[owenpkent]

Third follow-up, 859f351: each line is now its own captioned boxed card (LINE A / LINE B, outer LINES frame removed - a box around both was what made them read as one); RATE and SHAPE are named over their stepper pairs; the A/B/All tabs, BPM and Quantize moved to the ARP section bar (editor-owned, tabs hide on fold, still drop targets under the same accessible names); and a click on a chord card never feeds a line - drag is the only way in, with the cleared-card ring click kept as a release. Window is 1192 px, from 1450 at the start of the day.

[owenpkent]

Two more passes, cb701f2 and 1e9c2b6. The tempo is a plain Ableton-style number on the Controls bar (a Slider subclass that overrides paint, so no track/bar/knob is drawn, with < > for the click-only path); it left the Controls band entirely. Then Root, Scale, Scale Lock, Voices and MIDI Ch joined it there, leaving the band's first row as Size and Octave. That group did not fit at the editor's minimum width, so it has two sizes and measures which it can afford - captions drop first, which is what keeps the day the update button claims 170 px from starving the last combo to zero width. Off the Pads bar: the generator's Mode and Scale Compliance combos (still in the Generator window) and the arp target-line letter (the A/B tabs on the arp bar say it now). Dead code deleted rather than hidden. Both standalone targets build, 162 tests pass.