Typed coordinate entry for item placement (distance-from-wall + offset, AutoCAD-style)

Context

#308 added typed exact length while drafting walls (merged in #883). The next gap for precise placement: after a wall exists, placing items at exact distances still requires pixel-perfect mousing.

Cabinets already support typed dimensions (W/D/H) via the measurement pills + Tab cycling (#880-adjacent work in packages/nodes/src/cabinet/tool.tsx). What is missing is typed position: an AutoCAD-style two-field dynamic input where you type one axis, Tab to the second axis, then Enter to place.

Proposal

While a placement tool is active and a snap point/reference exists:

1. Typing a number opens a two-field inline input (X = distance along reference, Y = offset from it), like AutoCAD's dynamic input.
2. Tab toggles focus between fields; the inactive field keeps its live pointer-tracked value.
3. Enter commits placement at the typed coordinates.
4. Values accept the full parseMeasurement grammar (m/cm/mm/ft-in), consistent with #883.
5. Escape clears the fields first, then cancels the tool (same two-stage pattern as #883).

Implementation notes

• The typed-buffer store from #883 (packages/editor/src/store/use-wall-draft-typing.ts) is a proven base; generalize it to two fields with an active-field index.
• Same parity requirement as #883: 2D floorplan and 3D viewport must both get the behavior in one PR (wiki/architecture/tools.md).
• First candidates: cabinet/window/door placement against a wall.

Out of scope (for the first cut)

• Polar coordinate entry (distance + angle) — could reuse the same store later.
• Absolute X/Y world coordinates — the from-wall reference is what designers expect.

Happy to implement this if maintainers agree on the interaction shape.