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.

demo/smoke_zoom_out.mjs

@@ -0,0 +1,64 @@
+// v1.49.x: zoom goes below the base fit, the editor does not shift the plan.
+// - the stage height follows the MEASURED header, not a hard-coded 118px, so
+//   entering an editor keeps the plan inside the viewport;
+// - zoom < 1 centres the content instead of pinning it to a corner;
+// - the content frame (default zoom) includes devices standing outside rooms.
+import { launch, checkAll, finish } from './serve.mjs';
+const { page, browser } = await launch();
+const out = {};
+
+// -- editor entry keeps the stage inside the viewport --------------------
+const stageBox = () => page.evaluate(() => {
+  const sr = window.__card.shadowRoot || window.__card.renderRoot;
+  const b = sr.querySelector('.stage').getBoundingClientRect();
+  return { top: Math.round(b.top), bottom: Math.round(b.bottom) };
+});
+const vh = await page.evaluate(() => window.innerHeight);
+const inView = await stageBox();
+await page.evaluate(() => window.__card._setMode('plan'));
+await page.waitForTimeout(400);
+const inPlan = await stageBox();
+out.viewFitsViewport = inView.bottom <= vh + 2;
+out.editorFitsViewport = inPlan.bottom <= vh + 2; // used to overflow by ~90px
+out.editorStageShrinks = inPlan.top > inView.top && inPlan.bottom <= inView.bottom + 2;
+await page.evaluate(() => window.__card._setMode('view'));
+await page.waitForTimeout(300);
+
+// -- zoom out below the base fit -----------------------------------------
+out.zoomOut = await page.evaluate(() => {
+  const c = window.__card;
+  c._resetZoom();
+  const fit = { ...c._viewOr(c._baseVb()) };
+  const stage = (c.shadowRoot || c.renderRoot).querySelector('.stage');
+  c._zoomAt(stage.clientWidth / 2, stage.clientHeight / 2, 0.5);
+  const v = { ...c._view };
+  const base = c._baseVb();
+  const cx = v.x + v.w / 2, cy = v.y + v.h / 2;
+  return {
+    zoom: c._zoom,
+    wider: v.w > fit.w * 1.9,                                   // actually zoomed out
+    centredX: Math.abs(cx - (base[0] + base[2] / 2)) < 1,       // not pinned to a corner
+    centredY: Math.abs(cy - (base[1] + base[3] / 2)) < 1,
+  };
+});
+out.zoomOutWorks = out.zoomOut.zoom === 0.5 && out.zoomOut.wider
+  && out.zoomOut.centredX && out.zoomOut.centredY;
+delete out.zoomOut;
+out.floorIsHalf = await page.evaluate(() => { window.__card._resetZoom(); const c = window.__card;
+  c._applyView(0.1); return c._zoom; }) === 0.4; // clamped at the floor
+await page.evaluate(() => window.__card._resetZoom());
+
+// -- devices outside rooms stretch the default frame ---------------------
+out.devicesStretchFrame = await page.evaluate(() => {
+  const c = window.__card;
+  const cfg = JSON.parse(JSON.stringify(c._serverCfg));
+  cfg.spaces[0].plan_url = null; cfg.spaces[0].plan_aspect = null;
+  c._serverCfg = cfg; c._model = null;
+  const before = c._baseVb();
+  // walk one lamp far outside every room
+  c._layout = { ...c._layout, d_lamp: { s: 'f1', x: 0.99, y: 0.5 } };
+  const after = c._baseVb();
+  return after[0] + after[2] > before[0] + before[2] + 20; // right edge follows the lamp
+});
+
+await finish(browser, checkAll(out));