Add voipms-trunk service: US-only outbound PSTN, max 3 concurrent calls

Adds a VoIP.ms SIP trunk on top of asterisk-digital-ocean: IP-authenticated
trunk (no password stored), NANP-only outbound dialplan, a global 3-call
concurrent cap via GROUP()/GROUP_COUNT(), and inbound routing to one
extension. Config lives in its own include files rather than being
appended directly to pjsip.conf/extensions.conf, since Easy Asterisk fully
regenerates both from its own internal state — the includes are patched
into the vendor's generator functions so they survive that regeneration.

Wires the new service into setup.sh's is_installed() and README's services
table, and updates docs/pstn-calling-voipms-plan.md to reflect what's now
implemented vs. still open (spend/volume alerting, live-account
verification).

README.md

@@ -67,7 +67,7 @@ a ready-to-copy Caddy config snippet to `~/docker/caddy-snippets/`.
 | Group | Services |
 |-------|---------|
 | `base` | `net-tools`, `ncdu`, `git`, `curl`, `wget`, `htop`, `tree`, `zip`/`unzip`, `ca-certificates`, `gnupg`, `jq`, `rsync`; `glow` (terminal markdown reader, Charm apt repo); Docker CE + Compose plugin; `openssh-server` with GitHub/Launchpad SSH key import, optional password-auth lockdown, and SSH Host aliases; optional NetBird overlay network |
-| `homelab` | `caddy`, `crowdsec`, `authelia`, `homeassistant`, `asterisk`, `asterisk-digital-ocean`, `security-dashboard`, `sunshine` |
+| `homelab` | `caddy`, `crowdsec`, `authelia`, `homeassistant`, `asterisk`, `asterisk-digital-ocean`, `voipms-trunk`, `security-dashboard`, `sunshine` |
 | `utilities` | `actualbudget`, `ai-gpu`, `ai-stack`, `archivebox`, `changedetection`, `ddclient`, `filebrowser`, `fmd`, `gatus`, `homebox`, `iopaint`, `joplin`, `koha`, `magicmirror`, `mail-archiver`, `mattermost`, `mealie`, `meshcentral`, `n8n`, `nextcloud`, `ntfy`, `onlyoffice`, `paintplus`, `portainer`, `rustdesk`, `stirling-pdf`, `syncthing`, `traccar`, `unifi`, `uptimekuma`, `vaultwarden`, `watchyourlan`, `watchtower`, `wg-easy` |
 | `media` | `arm`, `audiobookshelf`, `calibre-web`, `emby`, `immich`, `jellyfin`, `lyrion` |
 | `cameras` | `frigate`, `frigate-audio`, `frigate-notify`, `sky-cam` |
@@ -92,6 +92,7 @@ homelab
   homeassistant
   asterisk
   asterisk-digital-ocean
+  voipms-trunk
   security-dashboard
   sunshine