fix: openings and markers keep their identity across a space switch (#525)

Lit reuses list nodes by position. The opening list and the device markers had
no keys, so on a space switch the leaf that held a slot kept its DOM node and
only changed values — and `.op-leaf` (transform) and `.op-arc`
(stroke-dashoffset) carry a 0.6 s transition, so the browser animated a door
that never moved: the new floor's leaf drove in from the previous floor's
opening angle. Measured on two spaces with a door in the same place and
opposite contact states: the node is reused, transform goes
`rotate(-90deg) → rotate(0deg)`, dash offset `0 → 125.66`, both transitions
`running`. The marker shell adds two more with its `box-shadow`.

Both lists are now rendered through `repeat(…, (item) => item.id, …)`, the
same lesson `glow-scene.ts` already learned for the Glow spots. The trap is
written where it starts — above the two transitions in `plan.styles.ts` —
because that is the file someone edits when adding the next animated property.
`houseplan-card.ts` is at its line ceiling, and the note would have cost the
budget a dozen lines for nothing: the swap itself is line-for-line.

The witness walks the shadow tree per element. `document.getAnimations()` is
empty here EVEN ON THE BROKEN CODE — the card lives in a shadow root and the
document-level call does not reach into it, and the issue proposed exactly
that call. The smoke also builds its own fixture: the demo home has no
openings at all, so two doors in two spaces are prepared in the smoke, and it
asserts the other half of the contract as well — a real contact change inside
one space still animates the leaf.

On `origin/dev` the smoke fails on five facts, naming the offenders:
`op-arc:stroke-dashoffset`, `op-leaf:transform`, `device-shell-frame:box-shadow`
twice. Mutants `openings-rendered-without-keys` and
`device-markers-rendered-without-keys` put each `map` back.

Perf, 7 samples against `19e421b3`: spaceSwitchMs 524.8 (limit 769.35, base
512.9), switchCycleMs 1293.9 (1696.28, 1256.5), firstStableRenderMs 2533.8
(3000, 2529.2), modelReadyMs 732.7 (944.97, 726.9), longTask.maxSingleMs 663
(910, 660) — `benchmark:compare` green in full.

The initial View graph grows 241 B gzip: `repeat` enters it for the first
time. The #438 ceiling is recentred 300 400 → 300 700 with the usual dated
note; measured 300 059 B keeps 641 B above and 1 359 B below the band. The
301 066 B budget is untouched, but only 366 B now separate the ceiling from
it — the #367 headroom debt has stopped being theoretical.

Issue: #525
User-Visible: yes

scripts/mutation-gate.mjs

@@ -7297,6 +7297,30 @@ const MUTANT_DEFINITIONS = [
       replace: '          this._loadOk = true;',
     }],
   },
+  {
+    id: 'openings-rendered-without-keys',
+    guard: 'node demo/smoke_space_switch_transitions.mjs',
+    because: 'Lit reuses list nodes by position: without a key the leaf of the next space '
+      + 'inherits the node of whatever door held that slot, and its 0.6s transform transition '
+      + 'animates a door that never moved (#525 AC1)',
+    patches: [{
+      file: 'src/houseplan-card.ts',
+      find: '    return svg`<g class="openinglayer">${repeat(items, (o) => o.id, (o) => {',
+      replace: '    return svg`<g class="openinglayer">${items.map((o) => {',
+    }],
+  },
+  {
+    id: 'device-markers-rendered-without-keys',
+    guard: 'node demo/smoke_space_switch_transitions.mjs',
+    because: 'the marker shell carries a `box-shadow` transition, so a positional reuse replays '
+      + 'it on every space switch; the key also keeps `data-id` honest for the live editor '
+      + 'painter, which finds the dragged marker by that attribute (#525 AC2)',
+    patches: [{
+      file: 'src/houseplan-card.ts',
+      find: '            ${repeat(devs, (d) => d.id, (d) => this._renderDevice(',
+      replace: '            ${devs.map((d) => this._renderDevice(',
+    }],
+  },
   {
     id: 'live-editor-devices-drops-align-guides',
     guard: 'node demo/smoke_align_guides.mjs',