perf/fix v1.43.1: external audit P1 — render cost, drag threshold, geometry, backend

L1: memoized space model + open pairs (structural fingerprint key, epoch
bumped synchronously at mutation time, not inside the debounce); hoisted
per-room geometry out of the render loop; smoke asserts zero recomputation
across state pushes.

L4: openings get the 3 px drag threshold used by every other pipeline and
only write when the geometry actually changed — taps open the dialog again.

G2: interiorPoint() replaces the vertex mean, so island rooms inside
concave (U/L) parents are accepted and their evenodd holes render; traced
duplicates still are not containment.

G3: segKey rounds before ordering — one shared wall, one key.

B2: _check_write fails closed when the entry is unavailable.
B3: layout/set honours expected_rev and returns the new rev.
B4: config/set without expected_rev over a non-empty store logs a warning.
B5: coordinates reject NaN/Infinity; spaces/rooms/markers/decor/layout capped.

+2 unit tests (118), +2 backend tests (14), smoke_render_perf; docs
same-commit

custom_components/houseplan/const.py

@@ -13,7 +13,7 @@ FILES_URL = "/houseplan_files/files"
 CONTENT_URL = "/api/houseplan/content"
 FILES_DIR = "houseplan/files"
 CONF_ADMIN_ONLY = "admin_only"
-VERSION = "1.43.0"
+VERSION = "1.43.1"
 
 DEFAULT_CONFIG: dict = {
     "spaces": [],