Emergency calling, stage 1: urn:service:sos with a digits fallback

Classify 112/911 (plus EMERGENCY_NUMBERS) at Dial. A classified call
INVITEs urn:service:sos over the existing registration and, on any
non-2xx final not caused by the user hanging up (including the
setup-timeout CANCEL paths), retries once as a plain INVITE of the
dialled digits — the pre-0.3.0 behavior, so classification can never
place a call worse than the status quo. The reverse edge: a 380
Alternative Service whose body carries the emergency indication
upgrades an unclassified call to the sos URN; a bare 380 stays an
error, since promoting an arbitrary redirect would put a
non-emergency call through to a PSAP. An emergency dial preempts an
in-progress call, and an answer racing a deadline-initiated CANCEL is
taken instead of BYE'd (user-initiated CANCEL races still BYE).

No emergency registration, no emergency PDN, no CS fallback, no
SIM-less calling, no AML — and no carrier has confirmed the sos path
end-to-end. The README warning states exactly that.

Assisted-by: Claude:claude-fable-5

packaging/APKBUILD

@@ -5,7 +5,7 @@
 # (or replaced here by a bootstrap invocation). Until then this documents
 # the packaging shape.
 pkgname=imsd
-pkgver=0.2.7
+pkgver=0.3.0
 pkgrel=0
 pkgdesc="Userspace IMS/VoLTE daemon for mainline Linux phones"
 url="https://forgejo.catcrafts.net/Catcrafts/imsd"