Admit kiosk callers by network position, not only by device token

The device token assumes a handful of fixed screens an administrator
provisions once. That is not how these kiosks are used: most people open the
page on their own PC, and there is no login, so per-browser provisioning would
mean touching every PC on the floor and losing it again on the next reimage or
cleared profile. A screen in that state did not look refused either - the USB
kiosk rendered a working page whose every call answered 404.

Both kiosks now admit a caller on either ground, the same shape the GE-Enforce
client endpoints already use: the per-device token, or a source address inside
an allowlist. Wall screens keep the token and are not confined to the
allowlist; everyone else is admitted by where they are on the network. Still
gated on the site's enable flag, so nothing opens by itself, and both
allowlists ship empty - token-only until a site enters its ranges.

- shopdb.api gains ip_in_cidrs and request_ip_allowlisted (contract 0.35.0).
  On the surface because both plugins need the identical gate, and a CIDR
  parser copied into two of them is where a fail-open creeps in later. They
  fail closed on an empty setting, an unparseable caller address and a
  malformed entry, and they read remote_addr rather than raw X-Forwarded-For -
  so the IIS rewrite rule is what makes them meaningful, which the module says
  at length.
- Separate settings per kiosk, usb_kiosk_allowed_cidrs and
  printedparts_kiosk_allowed_cidrs. One must not grant the other, for the same
  reason the tokens are separate.
- Both settings pages get a picker listing the network plugin's subnets with
  their VLANs. It stores resolved CIDR strings, not subnet ids: the setting has
  to work at a site that does not run that plugin and must not break when an
  inventory row is deleted. Entries matching no subnet are shown rather than
  hidden, since a stale one left by an inventory edit looks exactly like a
  hand-typed range.
- USBKiosk says it was not admitted instead of pretending to work, which
  PartsKiosk already did.
- The USB settings page keyed text-vs-boolean off the token alone. Adding a
  second text setting to the boolean path would have saved it as the word
  'true' - the bug that replaced the kiosk token and 404'd every provisioned
  screen. Both load and save now key off a list, with a spec on it.

The trade, stated plainly in the admin UI: anyone on an allowed network can
check a drive in or out against a badge number they guess, and the record
carries that person's name. Badges are attribution, not authorization. Keeping
the ranges narrow is what bounds it; login is the alternative and was ruled out
because these users do not sign in.

shopdb/api/__init__.py

@@ -187,6 +187,11 @@ from shopdb.utils.uploads import send_upload, harden_upload_response
 # nothing. See shopdb/utils/clientip.py.
 from shopdb.utils.clientip import client_ip, strip_port
 
+# Network-position allowlists for the unauthenticated kiosk routes. On the
+# contract surface because two plugins need the identical gate and a
+# copy-pasted CIDR parser is exactly where a fail-open creeps in.
+from shopdb.utils.ipallowlist import ip_in_cidrs, request_ip_allowlisted
+
 # Strict date parsing. On the contract surface because every plugin that stores
 # a date needs it and the two that rolled their own both swallowed the error.
 from shopdb.utils.queryargs import QueryArgError, intarg, intargs
@@ -477,6 +482,8 @@ __all__ = [
     'harden_upload_response',
     'client_ip',
     'strip_port',
+    'ip_in_cidrs',
+    'request_ip_allowlisted',
     # Import-mode helpers
     'apply_import_timestamps',
     'import_mode_active',