fix v1.43.0: external audit P0 — data loss, split geometry, auth, dialog zombies

L2 (silent data loss): debounce gains flush()/pending(); _reloadConfigOnly
flushes a pending write and defers while one is in flight; conflict path
forces; failed reload now toasts instead of an empty catch; teardown flushes.

G1 (split corruption): same-edge cuts carve the niche properly instead of
walking the outline twice; partition invariant (parts sum to the original)
rejects anything else; +1 unit test covering 5 niche shapes and both legacy
cut shapes.

B1 (unauthenticated content): plans and marker files move to
HouseplanContentView (/api/houseplan/content/..., requires_auth); only the
card bundle stays static; contentUrl() rewrites legacy URLs on read (no
storage migration); repairs.py accepts both prefixes; +1 unit test.

L3 (dialog zombies): all four save catch-blocks guard against a closed
dialog; the card no longer blanks when a save fails after Esc.

smokes: smoke_save_race, smoke_dialog_zombie; docs (TESTING/CHANGELOG/
ARCHITECTURE incl. the optimistic-UI note) same-commit

custom_components/houseplan/const.py

@@ -9,9 +9,11 @@ FRONTEND_URL = "/houseplan_files/houseplan-card.js"
 PLANS_URL = "/houseplan_files/plans"
 PLANS_DIR = "houseplan/plans"  # relative to the HA configuration directory
 FILES_URL = "/houseplan_files/files"
+# authenticated read path (audit B1): /api/houseplan/content/<plans|files>/<sub>/<name>
+CONTENT_URL = "/api/houseplan/content"
 FILES_DIR = "houseplan/files"
 CONF_ADMIN_ONLY = "admin_only"
-VERSION = "1.42.2"
+VERSION = "1.43.0"
 
 DEFAULT_CONFIG: dict = {
     "spaces": [],