Dedupe RING_EXTS before generating the inbound dialplan

Confirmed live: a ring-group list with a repeated extension ("201 301 313
312 313") generated duplicate ring<ext>/skip<ext> priority labels in the
same [from-pstn-trunk] extension. Asterisk doesn't error on this - it
silently resolves Goto() to the wrong occurrence and loops between the two
blocks forever, so the call never reaches the actual Dial() and nothing
ever rings, with no error to point at the cause. Dedupes (first-occurrence
order preserved) regardless of how the duplicate got in there.

services/pstn-trunk.sh

@@ -252,6 +252,14 @@ MEMBER
 # embedded-delimiter risk since every field here is digits/hostnames).
 _pstn_write_dialplan_include() {
     local FILE="$1" DID="$2" RING_EXTS="$3" NTFY_URL="$4"
+    # Dedupe: a repeated extension (typo, copy-paste, or a settings file
+    # edited by hand) would otherwise generate two identical ring<ext>/
+    # skip<ext> priority labels in the same [from-pstn-trunk] extension.
+    # Confirmed live: Asterisk doesn't error on the duplicate labels, it
+    # silently resolves Goto() to the wrong one and loops between the two
+    # blocks forever — the call never reaches the actual Dial(), and no
+    # ring/notification ever happens, with no error anywhere to point at it.
+    RING_EXTS="$(echo "$RING_EXTS" | xargs -n1 | awk '!seen[$0]++' | xargs)"
     cat > "$FILE" << 'EOF'
 ; PSTN outbound/inbound — US-only (NANP). Concurrent-call caps (both
 ; directions) AND tiered permissions (internal / restricted / full) are read