Vacuum first-use path: materialize the marker, count rectangle rooms, fix the toasts

Audit HP-1540-01 (High): an auto-discovered vacuum has no config marker
until the device dialog is saved once, yet the live-position section was
already interactive. setVac, _vacSaveMatrix and auto-calibration all did
cfg.markers.find(...) and silently bailed out — while the auto-calibration
toast still claimed success. Every vacuum edit now materializes a minimal
marker (same id/binding the dialog Save would produce), _vacSaveMatrix
reports whether the write landed, and success toasts are gated on it.

HP-1540-04: the auto-calibration room matcher accepted only polygon rooms
and told users their room names did not match. It goes through the shared
roomPoly() now, so legacy x/y/w/h rectangles count like everywhere else.

HP-1540-06: the no-rooms/no-match/rough-fit toasts pointed at the removed
point calibration; they now point at the fit panel that shipped instead,
and docs/VACUUM.md Setup UX describes the actual UI. Also extracted
vacMapIdFromAttrs as the explicit frontend half of the map-id contract
(backend half lands with HP-1540-02).

Regressions: demo/smoke_vacuum_firstuse.mjs starts from cfg.markers=[]
(the fixture gap the audit called out) with rectangle plan rooms and a
zero map_index, and fails 11 checks on the v1.54.0 bundle; i18n unit test
asserts no point/точк wording in either language.

test/vacuum.test.mjs

@@ -1,6 +1,6 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
-import { solveAffine, applyAffine, affineResidual, readVacTelemetry, autoCalibrate, thinPath, pushTrailPoint, isVacMoving, isVacSourceState } from '../test-build/vacuum.js';
+import { solveAffine, applyAffine, affineResidual, readVacTelemetry, autoCalibrate, thinPath, pushTrailPoint, isVacMoving, isVacSourceState, vacMapIdFromAttrs } from '../test-build/vacuum.js';
 
 test('solveAffine recovers rotation+scale+mirror+offset exactly', () => {
   // target = mirror-X, rotate 90°, scale 0.02, offset (300, 400)
@@ -135,3 +135,20 @@ test('fitMatrix/fitFromMatrix round-trip, mirror and quarters', async () => {
   const c2 = applyAffine(fitMatrix(r2), 500, 500);
   assert.ok(Math.abs(c2[0] - c[0]) < 1e-6 && Math.abs(c2[1] - c[1]) < 1e-6);
 });
+
+// HP-1540-02: the map-id contract, mirrored by trails.py resolve_map_id —
+// the first value that is not null/undefined wins; zero and '' are valid ids.
+test('vacMapIdFromAttrs: first NOT-nullish value wins, zero survives', () => {
+  assert.equal(vacMapIdFromAttrs({ map_index: 0 }), '0');
+  assert.equal(vacMapIdFromAttrs({ map_index: '0' }), '0');
+  assert.equal(vacMapIdFromAttrs({ map_name: '', selected_map: 'Floor' }), '');
+  assert.equal(vacMapIdFromAttrs({ map_name: 'A', map_index: 0 }), 'A');
+  assert.equal(vacMapIdFromAttrs({ current_map: 2 }), '2');
+  assert.equal(vacMapIdFromAttrs({ selected_map: 'Vac' }), 'Vac');
+  assert.equal(vacMapIdFromAttrs({}), 'default');
+});
+
+test('readVacTelemetry keeps numeric zero map_index as map id (HP-1540-02)', () => {
+  const t = readVacTelemetry({ vacuum_position: { x: 1, y: 2 }, map_index: 0 });
+  assert.equal(t.mapId, '0');
+});