feat(core,host): Wake-on-LAN sender + host MAC advertisement

Add a runtime-free Wake-on-LAN sender in punktfunk-core (per-interface subnet-directed broadcast + 255.255.255.255 on ports 9/7, repeated, optional last-known-IP unicast) exposed both as a Rust fn and a punktfunk_wake_on_lan C-ABI (ABI v3), plus a parse_mac helper. The host enumerates its wake-capable NIC MAC(s) and advertises them in a new mDNS `mac` TXT record (routed NIC first), and best-effort detects & warns (never modifies) when the NIC isn't armed for WoL.

MAC delivery is via the unauthenticated mDNS TXT rather than the connection handshake by design: a spoofed MAC only makes a wake fail (the packet is inert; the cert fingerprint still gates the connection), and it avoids threading through the hot connect path.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-core/Cargo.toml

@@ -38,6 +38,10 @@ thiserror = "2"
 tracing = { version = "0.1", default-features = false, features = ["std"] }
 rand = "0.9"
 zeroize = "1"
+# Interface enumeration for Wake-on-LAN: computes each NIC's subnet-directed broadcast so a
+# magic packet reaches the host's L2 segment on multi-homed clients (VPN/docker/multiple LANs),
+# not just the default route. Tiny, cross-platform (getifaddrs / GetAdaptersAddresses), no cmake.
+if-addrs = "0.13"
 
 quinn = { version = "0.11", optional = true }
 rustls = { version = "0.23", optional = true, default-features = false, features = ["ring", "std"] }