dialplan: build the dial string per contact; iOS Linphone's push params broke Dial

Its Contact holds pn-prid=...:voip&...:remote, and PJSIP_DIAL_CONTACTS passes that '&' through,
so Dial rejected the whole device list and the call dropped for every device of the user.
sp-sub-contacts walks the AOR's contacts, drops pn-* params and FILTERs the rest. call-test
registers a phone with such a Contact and checks it is rung.

CHANGELOG.md

@@ -3,6 +3,11 @@
 Versions follow [semver](https://semver.org). Each release's container images are built from its
 tag (08 §3.1): `selfphoneng-api` and `selfphoneng-asterisk`, on ghcr.io and on the Gitea registry.
 
+## Unreleased
+
+- Fix: calls to a user with Linphone on an iPhone registered dropped at once, for every device of
+  that user. Its push parameters hold `&`, which split the dial string.
+
 ## v0.0.1 — 2026-10-20
 
 The first tagged build, for testing. Not for production yet: the v1.0 definition of done