fix v1.44.4: audit follow-up B2, B5, L4 sub-item

B2: the HTTP upload view failed OPEN when the config entry was
unavailable while the WS path failed closed — both now share one
may_write() policy helper (new auth.py) that denies non-admins when the
policy cannot be read.

B5: _finite now guards room rects, polygon vertices, view_box and
opening coordinates, not just layout positions; the declared
MAX_OPENINGS cap is finally enforced.

L4 (sub-item): every drag pipeline captures the pointer through the
tolerant helper (an inactive pointerId used to kill device/label/resize
drags); decor shapes gained a bounds clamp so they cannot be dragged far
outside the plan and persisted there.

+2 backend tests (16); both changelogs updated in this commit

custom_components/houseplan/auth.py

@@ -0,0 +1,28 @@
+"""Single source of truth for the write-authorization policy.
+
+The WS and HTTP paths used to duplicate this decision and drifted apart: the
+WS copy was fixed to fail closed while the upload view still failed OPEN when
+the config entry was unavailable (audit follow-up B2, 2026-07-27). One helper,
+one behaviour.
+"""
+from __future__ import annotations
+
+from homeassistant.core import HomeAssistant
+
+from .const import CONF_ADMIN_ONLY
+from .store import get_entry
+
+
+def may_write(hass: HomeAssistant, user) -> bool:
+    """True when `user` may modify House Plan data.
+
+    Fails CLOSED: when the entry cannot be read — during a reload, or while the
+    integration is disabled — the policy is unknown, and "unknown" is not the
+    same as "permissive": only admins are allowed through.
+    """
+    is_admin = bool(getattr(user, "is_admin", False))
+    entry = get_entry(hass)
+    if entry is None:
+        return is_admin
+    admin_only = bool(entry.options.get(CONF_ADMIN_ONLY, False))
+    return is_admin if admin_only else True