feat(geo): allow an opt-in plain-HTTP location provider

A self-hoster can set IP_GEO_ALLOW_INSECURE=true alongside an http:// URL to
use a free HTTP-only provider — the free ip-api.com endpoint is HTTP-only (its
HTTPS form needs a paid key) but its geolocation is often more accurate and it
carries the ISP. The default stays HTTPS-only with ipwho.is; plain HTTP is
refused unless the operator explicitly opts in, since the looked-up IP then
travels unencrypted over the server's own egress. Whitelisted in compose and
documented in the env example.

docs/api/openapi.yaml

@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: HealthLog API
-  version: 1.25.5
+  version: 1.25.6
   description: >-
     Self-hosted personal-health-tracking PWA — public API surface for the iOS native client and external ingest.