zoom-out, device-aware content frame, and the editor no longer shifts the plan

Three owner reports:

- The content frame behind the default zoom only looked at rooms, and devices
  are allowed to stand outside every one of them — a gate sensor by the fence
  was left outside the opening view. contentBounds() takes the marker positions
  now, and they count as content even on a space with no rooms at all.

- Entering an editor 'strangely shifted' the plan. The stage height was
  100dvh minus a hard-coded 118px of header, and the editor header is ~90px
  taller than that: the whole scene slid down by the difference and its bottom
  went below the fold. The card now measures where the stage actually starts
  (HA toolbar, margins and our header included) and gives it the rest of the
  viewport; the measurement is deferred a frame because setting state straight
  from a ResizeObserver callback trips the 'undelivered notifications' error,
  which smoke_dialog_zombie rightly counts as a page error.

- Zoom stopped at the base fit. The floor is 0.4× now, and zoomed out the
  clamp centres the content instead of pinning it to the top-left corner —
  with the view larger than the plan there is nothing to clamp against.

New smoke: smoke_zoom_out.mjs (editor keeps the stage inside the viewport,
0.4 floor, centring, the device-stretched frame); a unit test for the extra
points of contentBounds. Not released — the next release goes out after the
v1.49.0 audit.

test/space-geometry.test.mjs

@@ -106,3 +106,20 @@ test('contentBounds: fits what is drawn, with a 5% margin', () => {
   const empty = spaceModels({ spaces: [{ id: 's', view_box: [0, 0, 1, 1], rooms: [] }], markers: [] })[0];
   assert.equal(contentBounds(empty), null);
 });
+
+test('contentBounds: devices outside every room stretch the frame', () => {
+  const one = spaceModels({ spaces: [{
+    id: 's', view_box: [0, 0, 1, 1],
+    rooms: [{ id: 'r', poly: [[0.4, 0.4], [0.6, 0.4], [0.6, 0.6], [0.4, 0.6]] }],
+  }], markers: [] })[0];
+  // a gate sensor far to the right of the room
+  const b = contentBounds(one, 0.05, [[900, 500]]);
+  // span 400..900 wide, 400..600 tall; margin 5% of the larger side (500)
+  assert.deepEqual(b, { x: 375, y: 375, w: 550, h: 250 });
+  // devices alone are content enough — an empty yard with two cameras
+  const empty = spaceModels({ spaces: [{ id: 's', view_box: [0, 0, 1, 1], rooms: [] }], markers: [] })[0];
+  const only = contentBounds(empty, 0.05, [[100, 100], [300, 200]]);
+  assert.equal(Math.round(only.w), 220);
+  // and junk coordinates are ignored, not spread across the canvas
+  assert.deepEqual(contentBounds(one, 0.05, [[NaN, 5]]), contentBounds(one));
+});