Make TURN/STUN port configurable via TURN_PORT env var

UniFi controller uses UDP 3478 for STUN, preventing coturn from
binding. Add TURN_PORT variable (default 3478) so users can set
TURN_PORT=3479 in .env to avoid the conflict.

https://claude.ai/code/session_01Vm6NLaQuzM4VosAotqS1q8

.env.example

@@ -8,9 +8,9 @@
 #   4. docker exec -it easy-asterisk easy-asterisk
 #
 # Port forwarding required on your router:
-#   5061/tcp   → SIP TLS signaling
-#   3478/udp   → STUN/TURN (NAT traversal + media relay)
-#   3478/tcp   → TURN TCP fallback (for restrictive networks)
+#   5061/tcp        → SIP TLS signaling
+#   3478/udp+tcp    → STUN/TURN (NAT traversal + media relay)
+#                     (change with TURN_PORT if 3478 is taken)
 #   10000-20000/udp → RTP media (or your custom range below)
 #
 # How it works:
@@ -58,7 +58,7 @@ LOCAL_CIDR=
 HAS_VLANS=n
 VLAN_SUBNETS=
 
-# ── TURN/STUN Credentials ────────────────────────────────────
+# ── TURN/STUN Settings ──────────────────────────────────────
 # Used by coturn for TURN relay authentication.
 # If TURN_PASSWORD is empty, a random password is generated on
 # first startup and saved to /etc/easy-asterisk/config.
@@ -68,6 +68,12 @@ VLAN_SUBNETS=
 TURN_USERNAME=easyasterisk
 TURN_PASSWORD=
 
+# ── TURN/STUN Port ──────────────────────────────────────────
+# Default: 3478 (standard STUN/TURN port)
+# Change if 3478 is already in use (e.g., UniFi controller uses 3478/udp).
+# Common alternative: 3479
+TURN_PORT=3478
+
 # ── TURN Relay Port Range ─────────────────────────────────────
 # Ports coturn uses for media relay. Forward this range on your router.
 # Default is 100 ports (enough for ~50 simultaneous relayed calls).