feat v1.31.0: room cards — metrics line + proportional resize

- room label becomes a card: name on top, optional metrics below
  (temperature / humidity / avg zigbee / lights), four checkboxes in
  space settings, all off by default; lights render On/Off or '1 of 3'
- areaHum + areaLightStats pure helpers (+3 unit tests, 90 total)
- resize via corner handles in the Plan editor (hover), uniform 0.5-3x,
  scale stored as layout k next to the position; drag preserves it
- fix latent v1.25 regression: draggable HTML labels were never rendered
  in the Plan editor (static SVG only) — real name-only cards now render
  there, draggable and resizable
- repair merge/split smokes still calling removed _toggleMarkup
- validation.py: 4 label_* bools; smoke_room_cards.mjs; docs same-commit

demo/smoke_merge_split.mjs

@@ -16,7 +16,7 @@ const S = () => page.evaluate(() => {
   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 enter = (t) => page.evaluate((t)=>{const c=window.__card; if(!c._markup)c._setMode('plan'); c._tool=t; return true;}, t);
 const out = {};
 
 // MERGE living(r1)+kitchen(r2) — share wall x=0.55, y∈[0.05..0.45]