Discover the party board's children from the household roster (Feature 20)

The board rendered nothing until a parent hand-wrote child_order with
each child's slug — the DAKOS bring-up gap. The household rollup now
publishes an ordered child_roster attribute (snapshot sort_order, each
entry carrying the slug the way HA derives entity ids, so the card can
build sensor.nestquest_<slug>_...), and the card discovers its plates
from it when the config carries no child_order; a supplied child_order
still wins. The rollups' existing per-child children counts attribute
is unchanged. Render tests drive the committed bundle under jsdom, so
the discovery contract is asserted on the artifact HACS ships.

frontend/package.json

@@ -9,6 +9,7 @@
     "lit": "^3.3.0"
   },
   "devDependencies": {
+    "jsdom": "^30.1.1",
     "typescript": "^5.9.2",
     "vite": "^7.1.5"
   }