feat(floorplan-editor): React rewrite + live in-room preview + UX polish

Complete modernization of the floor-plan editor. Three layered
changes shipped together since they share state shapes and the
test infrastructure stubs.

1) React rewrite (state + hooks + views + tests)

   Drops the FloorplanEditorContext singleton + legacy view
   components and replaces them with a pure-React reducer
   architecture:

   - state/ — typed FloorplanState + FloorplanAction union,
     pure reducer covering PAINT_TILE / ERASE_TILE /
     ADJUST_HEIGHT / SET_DOOR / SET_DOOR_DIR / SET_THICKNESS /
     SET_WALL_HEIGHT / BRUSH_SET / SELECT_RECT / SELECT_ALL /
     CLEAR_SELECTION / SQUARE_SELECT_TOGGLE / IMPORT_STRING /
     APPLY_REMOTE_DIFF / APPLY_REMOTE_SNAPSHOT. Source-tagged
     ('local' | 'remote') so the editor can distinguish user
     edits from server pushes. Co-located encoding helpers
     (parseTilemap / serializeTilemap) and area-counter
     selectors.
   - hooks/ — useFloorplanReducer (wraps useReducer with a
     history stack + loadFromServer + undo/redo), useTool
     (pointer events -> dispatch), usePointerToTile (screen
     -> tile projection that respects the viewBox origin so
     pan/zoom stays accurate).
   - views/ — FloorplanCanvasSVG, FloorplanHeightPicker,
     FloorplanToolbar, FloorplanOptionsPanel,
     FloorplanImportExport, FloorplanTile,
     FloorplanPreviewSVG (alternative iso preview kept as a
     fallback view, not wired into the main layout).
   - Co-located Vitest suites for every module above (encoding,
     reducer, selectors, hooks, views, integration). 100+ new
     test cases.

2) Live in-room preview (NEW capability)

   useFloorplanLiveSync drives client-side preview of the edit
   directly into the active room — every tile / door / wall
   height / thickness change is applied through
   GetRoomMessageHandler().applyFloorModelLocally (new public
   method on the renderer, see paired renderer PR) with
   zero server traffic during editing. The wire
   UpdateFloorPropertiesMessageComposer is only sent when the
   user explicitly clicks Save. Thickness slider additionally
   calls RoomEngine.updateRoomInstancePlaneThickness for
   zero-latency wall/floor-depth feedback while dragging.

   Toggle 'Live preview ON / OFF' in the bottom strip (default
   ON) lets the user opt out if they want to keep changes
   contained to the editor's own preview until Save.
   Revert button re-applies the original snapshot locally so
   the room snaps back to where it was when the editor opened.

3) UX polish

   - Undo / Redo (Ctrl+Z, Ctrl+Shift+Z / Ctrl+Y) backed by a
     100-step history stack inside useFloorplanReducer. Local
     mutating actions push history; brush/selection UI bumps
     and remote dispatches bypass it; loadFromServer wipes the
     stack.
   - Zoom 40-600 % with Ctrl+wheel, +/- buttons, % label.
     Shift+drag or middle-mouse drag pans the canvas.
   - Auto-fit on first paint: computes the screen-space
     bounding box of the painted (non-blocked) tiles, picks the
     zoom that just contains them with a 5 % margin, pans so
     the room sits in the viewport centre. Default view is now
     'room fills the canvas' instead of 'room is a dot at the
     top-centre of a huge empty canvas'. Clicking the % label
     re-runs the fit; crosshair button keeps zoom and recentres
     the pan only.
   - Door direction control: arrows + door icon triplet
     (8-way rotate by single click on prev/next, full cycle
     forward on the icon itself). Wall and floor thickness
     collapse from two 4-button rows into two compact
     segmented selectors (active state in emerald). Saves
     significant horizontal space.
   - Habbo floor pattern tile (~186 B PNG, vendored from
     habbofurni.com/images/furni_floor.png) tiled as the
     canvas background with image-rendering: pixelated so the
     texture stays crisp at every zoom level. Replaces the
     solid black background.

Test infrastructure

   nitro-renderer.mock grows constructors / proxies / functions
   for everything the new floor-editor tests transitively
   import (floor composers + events, RoomEngineEvent,
   ILinkEventTracker, convertNumbersForSaving /
   convertSettingToNumber, GetRoomMessageHandler,
   GetTicker, GetRenderer, NitroTicker, RoomPreviewer with a
   sufficiently real .updatePreviewModel / dispose surface,
   and a TextureUtils.createRenderTexture that returns an
   object with a no-op .destroy). test-setup adds a no-op
   ResizeObserver polyfill (jsdom doesn't ship one and the
   optional FloorplanRoomPreview observes its container) and
   a draggable-windows-container portal root for tests that
   mount NitroCardView.

Files: 44 changed (mostly new). yarn typecheck 0 errors,
yarn test 341/341 green.

src/components/floorplan-editor/hooks/usePointerToTile.ts

@@ -0,0 +1,52 @@
+import { RefObject, useCallback, useMemo } from 'react';
+import { TILE_SIZE } from '../state/constants';
+
+const X_OFFSET = 1024;
+
+export const tileToScreen = (row: number, col: number): [number, number] =>
+{
+    const x = (col * TILE_SIZE / 2) - (row * TILE_SIZE / 2) + X_OFFSET;
+    const y = (col * TILE_SIZE / 4) + (row * TILE_SIZE / 4);
+    return [ x, y ];
+};
+
+export const screenToTile = (x: number, y: number): [number, number] =>
+{
+    const tx = x - X_OFFSET;
+    const col = ((tx / (TILE_SIZE / 2)) + (y / (TILE_SIZE / 4))) / 2;
+    const row = ((y / (TILE_SIZE / 4)) - (tx / (TILE_SIZE / 2))) / 2;
+    return [ row, col ];
+};
+
+type ViewBox = { width: number; height: number; x?: number; y?: number };
+
+export type PointerProjection = {
+    fromClient: (clientX: number, clientY: number) => { row: number; col: number } | null;
+};
+
+export const usePointerToTile = (
+    svgRef: RefObject<SVGSVGElement | null>,
+    viewBox: ViewBox
+): PointerProjection =>
+{
+    const { width, height, x: viewX = 0, y: viewY = 0 } = viewBox;
+
+    const fromClient = useCallback((clientX: number, clientY: number) =>
+    {
+        const svg = svgRef.current;
+        if(!svg) return null;
+        const rect = svg.getBoundingClientRect();
+        if(rect.width === 0 || rect.height === 0) return null;
+        // Map screen-space pointer onto the viewBox interior, then
+        // shift by the viewBox origin — when zoomed in the viewBox
+        // starts at (viewX, viewY) instead of (0, 0), so a pointer
+        // at the left edge of the SVG corresponds to viewX in
+        // local SVG units, not 0.
+        const localX = viewX + ((clientX - rect.left) / rect.width) * width;
+        const localY = viewY + ((clientY - rect.top) / rect.height) * height;
+        const [ row, col ] = screenToTile(localX, localY);
+        return { row: Math.round(row), col: Math.round(col) };
+    }, [ svgRef, width, height, viewX, viewY ]);
+
+    return useMemo(() => ({ fromClient }), [ fromClient ]);
+};