feat(editor): перетаскивание кнопки настроек комнаты (#645)

Кнопка сохраняет положение в пределах комнаты только на время сессии редактора,
корректно отменяется при pinch/cancel и учитывается подписями Resize.

Issue: #645
User-Visible: yes

test/room-gear-drag.test.mjs

@@ -0,0 +1,44 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  clampRoomGearPointAlongPath,
+  resolveRoomGearCenter,
+  roomGearDragMoved,
+  roomGearPointAllowed,
+} from '../test-build/room-gear-drag.js';
+
+const SQUARE = [[0, 0], [10, 0], [10, 10], [0, 10]];
+const L_SHAPE = [[0, 0], [10, 0], [10, 4], [4, 4], [4, 10], [0, 10]];
+
+test('#645 resolves an allowed temporary centre and rejects a stale one', () => {
+  const room = { id: 'room', name: 'Room', area: null, poly: SQUARE };
+  assert.deepEqual(resolveRoomGearCenter(room, [8, 7]), {
+    point: [8, 7], usedTemporary: true,
+  });
+  const stale = resolveRoomGearCenter(room, [12, 7]);
+  assert.equal(stale.usedTemporary, false);
+  assert.ok(roomGearPointAllowed(stale.point, SQUARE));
+});
+
+test('#645 keeps the click/drag threshold in CSS pixels', () => {
+  assert.equal(roomGearDragMoved([100, 100], [102, 101]), false);
+  assert.equal(roomGearDragMoved([100, 100], [102.01, 101]), true);
+  assert.equal(roomGearDragMoved([100, 100], [100, 96.9]), true);
+});
+
+test('#645 stops at the first room boundary', () => {
+  assert.deepEqual(clampRoomGearPointAlongPath([5, 5], [15, 5], SQUARE), [10, 5]);
+  assert.deepEqual(clampRoomGearPointAlongPath([5, 5], [8, 8], SQUARE), [8, 8]);
+});
+
+test('#645 cannot jump across a concave room cut-out', () => {
+  // Both endpoints are in the L-shaped room, but the direct segment crosses
+  // its missing top-right quadrant. The first intersection is (4, 6).
+  assert.equal(roomGearPointAllowed([2, 8], L_SHAPE), true);
+  assert.equal(roomGearPointAllowed([8, 2], L_SHAPE), true);
+  assert.deepEqual(clampRoomGearPointAlongPath([2, 8], [8, 2], L_SHAPE), [4, 6]);
+});
+
+test('#645 permits movement along the room boundary', () => {
+  assert.deepEqual(clampRoomGearPointAlongPath([0, 2], [0, 8], SQUARE), [0, 8]);
+});