v1.50.3: sizes are not coordinates (HP-1502-01)

The ±4 bound from v1.50.2 measured view_box[2:4] and room w/h with the same
ruler as coordinates, so zero and negative sizes still passed the schema —
and viewBox='0 0 0 0' draws nothing on every client, with the static card
computing aspect-ratio: 0 / 0 on top. _EXTENT now requires strictly positive
sizes with a floor of one thousandth of the canvas (1 render unit — far
below any real room, keeps the maths finite); coordinates stay allowed to be
negative, a crop origin legitimately sits past the edge.

Defensive layer for stores that already hold a broken viewport: spaceModels
falls back to the whole canvas — both cards render from that model, so both
get the fallback — and a legacy rectangle with a negative size reads as the
same rectangle drawn from the other corner.

Also: the room settings button is the bottom row of the room card, and the
room name renders in the same spot in view and plan modes (owner's request,
committed earlier on dev).

test/space-geometry.test.mjs

@@ -165,3 +165,21 @@ test('contentBounds: never degenerate, never unbounded (HP-1500-03)', () => {
   }], markers: [] })[0];
   assert.equal(contentBounds(allBad), null, 'the caller keeps the full canvas');
 });
+
+test('spaceModels: a stored broken view_box falls back to the canvas (HP-1502-01)', () => {
+  // the server refuses these now, but a store may already hold one
+  for (const vb of [[0, 0, 0, 0], [0, 0, -1, -2], [0, 0, 1], null, [0, 0, NaN, 1]]) {
+    const m = spaceModels({ spaces: [{ id: 's', view_box: vb, rooms: [] }], markers: [] })[0];
+    assert.deepEqual(m.vb, [0, 0, 1000, 1000], JSON.stringify(vb) + ' falls back');
+  }
+  // a legitimate crop viewport is preserved
+  const crop = spaceModels({ spaces: [{ id: 's', view_box: [0.1, 0.2, 0.5, 0.4], rooms: [] }], markers: [] })[0];
+  assert.deepEqual(crop.vb, [100, 200, 500, 400]);
+  // a legacy rect with a negative size is the same rectangle from the other corner
+  const m = spaceModels({ spaces: [{
+    id: 's', view_box: [0, 0, 1, 1],
+    rooms: [{ id: 'r', x: 0.6, y: 0.7, w: -0.2, h: -0.3 }],
+  }], markers: [] })[0];
+  const r = m.rooms[0];
+  assert.deepEqual([r.x, r.y, r.w, r.h].map(Math.round), [400, 400, 200, 300]);
+});