refactor(iso): drop the unused stageSize from the overlay fit input (#741)

Since #713 the overlay fit envelope reserves no nudge budget, and since
#725 _isoScene passes `stageSize: null` while resolveIsoOverlayFitEnvelope
never reads the field. The room focus still built a { width, height }
object from the stage for nothing. The optional field is removed from
IsoOverlayFitEnvelopeInput together with both call-site arguments.

The #725 AC3 unit compared bounds with stageSize null and 1000x500, which
is now meaningless; it checks instead that the fit bounds follow only
scene.frame and the tiles: the same bounds for every stage aspect, a moved
frame moves them, an enclosing frame is returned as is.

Issue: #741
User-Visible: no
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018qZfe7YS4rqEMKoVeS3GKd

src/houseplan-card.ts

@@ -6004,7 +6004,7 @@ export class HouseplanCard extends LitElement {
       disp, runtime.resolveIsoDecorationLayers(disp), scene, iconPct, effectiveDeviceBaseSize(iconPct),
       disp.showLqi ?? this._config?.show_signal ?? true);
     const envelope = overlays && runtime.resolveIsoOverlayFitEnvelope({
-      baseBounds: scene.frame, entries: overlays.entries, stageSize: null, targetView: (bounds) =>
+      baseBounds: scene.frame, entries: overlays.entries, targetView: (bounds) =>
         fitView([bounds.x, bounds.y, bounds.w, bounds.h], aspect) });
     return envelope ? { ...scene, frame: envelope.bounds, overlayFitEntries: overlays.entries } : scene;
   }
@@ -6192,8 +6192,7 @@ export class HouseplanCard extends LitElement {
     const runtime = this._isoSceneRuntime, entries = this._renderIsoScene?.overlayFitEntries;
     if (target && this._effectiveProjection() === 'iso' && runtime && entries?.length) {
       const envelope = runtime.resolveIsoOverlayFitEnvelope({
-        baseBounds: bounds, entries, ownerId: room.id, stageSize: {
-          width: stage.clientWidth, height: stage.clientHeight },
+        baseBounds: bounds, entries, ownerId: room.id,
         targetView: (fitBounds) => targetOf(fitBounds)?.viewBox ?? null });
       if (envelope) { bounds = envelope.bounds; target = targetOf(bounds); }
     }

src/iso-scene-render.ts

@@ -648,7 +648,6 @@ export function isoOverlaySceneBounds(
 export interface IsoOverlayFitEnvelopeInput {
   baseBounds: Rect;
   entries: readonly IsoOverlayRenderEntry[];
-  stageSize?: { width: number; height: number } | null;
   targetView(bounds: Rect): Rect | null;
   ownerId?: string;
 }