fix+docs v1.21.1: audit of v1.16-v1.21

- fix: Split snaps the click to the room's nearest wall instead of the grid, so
  it works on non-grid-aligned rooms (imported/legacy polygons); the pull is
  capped (~6 cells) so accidental mid-room clicks stay a miss; splitRoom() still
  rejects a bad cut. closestPointOnBoundary() + unit test.
- docs: README (en+ru) documents Merge/Split/ruler/per-space scale (were undocumented);
  TESTING.md merge/split rows + fresh self-run; new smokes smoke_merge_split,
  smoke_split_nonsnap (incl. the capped-pull case).
- 73 frontend + 12 backend tests green; module eval + both cards register.

demo/smoke_merge_split.mjs

@@ -0,0 +1,83 @@
+// Merge & split room ops (v1.21.0) via the card's markup handlers (norm coords).
+import { launch } from './serve.mjs';
+const { page, browser } = await launch();
+const snap = await page.evaluate(() => JSON.stringify(window.__card._serverCfg));
+const restore = () => page.evaluate((s) => {
+  const c = window.__card; c._serverCfg = JSON.parse(s);
+  c._mergeSel = null; c._mergeDialog = null; c._splitSel = null; c._pendingSplit = null; c._roomDialog = false;
+  c._regSignature = ''; c._maybeRebuildDevices(); c.requestUpdate(); return c.updateComplete && true;
+}, snap);
+// norm→render helper mirrors what _markupClick passes to handlers
+const R = (nx, ny) => page.evaluate(([nx, ny]) => {
+  const c = window.__card; const H = 1000 / c._curSpaceCfg.aspect; return [nx * 1000, ny * H];
+}, [nx, ny]);
+const S = () => page.evaluate(() => {
+  const c = window.__card;
+  return { rooms: c._serverCfg.spaces.find((s) => s.id==='f1').rooms.map((r)=>({id:r.id,name:r.name,area:r.area})),
+    mergeDlg: !!c._mergeDialog, roomDlg: !!c._roomDialog, pendingSplit: !!c._pendingSplit, toast: c._toast };
+});
+const enter = (t) => page.evaluate((t)=>{const c=window.__card; if(!c._markup)c._toggleMarkup(); c._tool=t; return true;}, t);
+const out = {};
+
+// MERGE living(r1)+kitchen(r2) — share wall x=0.55, y∈[0.05..0.45]
+await enter('merge');
+await page.evaluate((p)=>window.__card._mergeClick(p), await R(0.3,0.3));
+await page.evaluate((p)=>window.__card._mergeClick(p), await R(0.75,0.25));
+out.mergeDialog = (await S()).mergeDlg;
+await page.evaluate(()=>window.__card._commitMerge());
+let s = await S();
+out.mergeRooms = s.rooms.length;                          // 4→3
+out.mergeKeptR1 = s.rooms.some(r=>r.id==='r1');
+out.mergeDroppedR2 = !s.rooms.some(r=>r.id==='r2');
+await restore();
+
+// MERGE non-adjacent: living(r1)+garden's-only? use r2+r4 (kitchen & hallway don't share a wall)
+await enter('merge');
+await page.evaluate((p)=>window.__card._mergeClick(p), await R(0.75,0.25)); // kitchen
+await page.evaluate((p)=>window.__card._mergeClick(p), await R(0.3,0.8));   // hallway
+s = await S();
+out.nonAdjRefused = !s.mergeDlg && s.rooms.length===4;
+out.nonAdjToast = !!s.toast;
+await restore();
+
+// grid-aligned test room (real rooms are snapped; demo rooms are not)
+await page.evaluate(()=>{
+  const c=window.__card;
+  c._serverCfg.spaces.find(s=>s.id==='f1').rooms.push(
+    {id:'rg', name:'GridRoom', area:null, poly:[[0.05,0.0625],[0.5,0.0625],[0.5,0.5],[0.05,0.5]]});
+  c._regSignature=''; c._maybeRebuildDevices(); c.requestUpdate();
+});
+// SPLIT rg vertical chord x=0.25 (all on grid nodes)
+await enter('split');
+await page.evaluate((p)=>window.__card._splitClick(p), await R(0.28,0.28));  // pick rg
+await page.evaluate((p)=>window.__card._splitClick(p), await R(0.25,0.0625)); // wall pt a
+await page.evaluate((p)=>window.__card._splitClick(p), await R(0.25,0.5));  // wall pt b
+out.splitPending = (await S()).pendingSplit;
+out.splitDialog = (await S()).roomDlg;
+// cancel keeps it whole
+await page.evaluate(()=>window.__card._roomDialogCancel());
+out.cancelWhole = (await S()).rooms.length===4;
+// redo + confirm with a name (no area)
+await page.evaluate((p)=>window.__card._splitClick(p), await R(0.28,0.28));
+await page.evaluate((p)=>window.__card._splitClick(p), await R(0.25,0.0625));
+await page.evaluate((p)=>window.__card._splitClick(p), await R(0.25,0.5));
+await page.evaluate(()=>{const c=window.__card; c._nameSel='Cabinet'; c._saveRoomNoArea();});
+s = await S();
+out.splitRooms = s.rooms.length;                          // 5
+out.bigKeepsLiving = s.rooms.some(r=>r.id==='r1' && r.area==='living_room');
+out.newRoom = s.rooms.find(r=>!['r1','r2','r3','r4','rg'].includes(r.id))?.name;
+await restore();
+
+// SPLIT along a wall → refused (both pts on top wall of rg)
+await page.evaluate(()=>{const c=window.__card; c._serverCfg.spaces.find(s=>s.id==='f1').rooms.push(
+  {id:'rg2', name:'G2', area:null, poly:[[0.05,0.0625],[0.5,0.0625],[0.5,0.5],[0.05,0.5]]});
+  c._regSignature=''; c._maybeRebuildDevices();});
+await enter('split');
+await page.evaluate((p)=>window.__card._splitClick(p), await R(0.28,0.28));
+await page.evaluate((p)=>window.__card._splitClick(p), await R(0.1,0.0625));
+await page.evaluate((p)=>window.__card._splitClick(p), await R(0.4,0.0625));
+s = await S();
+out.alongWallRefused = !s.roomDlg && !s.pendingSplit;
+
+console.log(JSON.stringify(out,null,1));
+await browser.close();