fix(openwrt): bind UDP dual-stack [::]:2121 so access-SSID clients reach it

The shipped router config bound the UDP transport "0.0.0.0:2121" (IPv4
wildcard) while the mDNS LAN advert announces every interface address,
including the router's IPv6 link-local — which phones on the !FIPS
access SSID rightly prefer (their cellular default route swallows v4,
and fd00::/8 is captured by the Myco mesh TUN). Result: the client's
Noise msg1 arrives on an unbound v6 port and is silently lost; the
handshake resends and times out.

Symptom chain (observed on-device): mDNS resolve OK, platform push OK,
"Sent Noise handshake message 1" to [fe80::…%N]:2121, four resends, no
reply, 30 s stale-timeout.

OpenWrt is Linux (bindv6only=0), so "[::]" accepts IPv4 via v4-mapped
addresses too — nothing is lost. packaging/common is deliberately left
on "0.0.0.0" for now: Windows defaults IPV6_V6ONLY=1, where "[::]"
would drop v4 instead.

packaging/openwrt-ipk/files/etc/fips/fips.yaml

@@ -72,7 +72,11 @@ dns:
 
 transports:
   udp:
-    bind_addr: "0.0.0.0:2121"
+    # Dual-stack wildcard, not "0.0.0.0": access-SSID clients (phones) learn
+    # this node's addresses from the mDNS advert and prefer the IPv6
+    # link-local — a v4-only bind silently drops their Noise msg1.
+    # OpenWrt is Linux (bindv6only=0), so "[::]" accepts v4 too.
+    bind_addr: "[::]:2121"
     # advertise_on_nostr: true
     # public: false # false => advertise udp:nat; true => advertise bound host:port
     # accept_connections: true # default; refuse inbound msg1 when false