Circuit-Editor Multi-Target Gate Support

[Scott Carda (ScottCarda-MS)]

Circuit Editor: multi-target / group drag-editing

Adds drag-editing for multi-wire gates in the circuit-vis circuit editor:
move multi-target gates and groups as rigid units, clone them as a unit
(Ctrl-drag), and extend a group onto new wires (Shift-drag). Purely additive on
top of the existing single-target editing paths.

What's new

• Rigid unit-move. Dragging a multi-target gate or group shifts the gate's
  own registers and every register in its child grid by the same delta, so the
  box and its contents stay aligned. Classical controls anchor correctly
  (external measurement refs stay put, internal ones move with the subtree), and
  a shift that would push any wire below 0 is refused without mutating the model.
• Clone-as-unit (Ctrl-drag). Leaves the source in place and drops a full
  copy at the target, using the same child-register remap as a unit-move.
• Shift-to-extend (Shift-drag). Dragging a child out of an expanded group
  offers dropzones on wires outside the group's span and paints a ghost border
  showing the extended bounds, growing the group onto new wires.

Changes

Area	File	What it adds
Source	actions/circuit-actions/move.ts	moveAsUnit, shiftAllRegisters, subtree wire-swap helpers, and the unit-shift branch of moveY.
Source	actions/circuitActions.ts	Unit-shift wire-growth/bounds in moveOperation; clone-as-unit + sourceWire param in addOperation.
Source	editor/controllers/dragController.ts	Shift-extend lifecycle (setup / spawn dropzones / paint ghost / tear down) and the multi-leg dropzone loop.
Source	editor/draggable.ts	makeShiftExtendGhost geometry helper.
Docs	ux/circuit-vis/README.md	Documents the transient single-gesture shift-extend state on DragController.
Tests	4 files under test/circuit-editor/	25 new tests (see below).

Testing

25 new circuit-editor tests, all passing: 7 clone-as-unit, 7 rigid unit-move /
bounds, 7 shift-extend lifecycle, 4 ghost-geometry.

# from source/npm/qsharp/
npm run build:ux
node --test "test/circuit-editor/**/*.test.mjs"