Step 2a (1/2): mDNS hostname.local and _http._tcp

- aes67_net: espressif/mdns 1.13.1 (managed component, pinned in
  dependencies.lock). Advertises <net.hostname>.local and the web UI as
  _http._tcp port 80. net apply callback renames live.
- First config value actually applied: net.hostname.
- Docs: mDNS in the core Network section; build order gets step 2a
  (mDNS, then LLDP).
- Verified on board: p4-aes67.local resolves via raw mDNS and getent,
  http://p4-aes67.local/ answers, service shows in _http._tcp browse;
  live rename to p4-rename and back works (after ~1 s probing).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/aes67-core-base.md

@@ -91,6 +91,7 @@ When this device is the GM, offset/frequency/delay show "–".
 ## Network
 - Default: one untagged interface. VLAN split option: AES67 untagged + internet tagged (inet.vlan_id/pcp) using the ESP-IDF vlan_support approach (examples/network/vlan_support, ESP32-P4 supported). AES67 side has no gateway; default route and DNS are on inet.
 - PTP, RTP, SAP and IGMP bind to the AES67 netif. HTTP server filters on `web_on`.
+- mDNS (espressif/mdns): `<net.hostname>.local` plus the web UI as `_http._tcp` port 80. A hostname change applies live (the new name answers after ~1 s of RFC 6762 probing).
 - Switch port: AES67 as native/untagged VLAN, internet tagged, PoE on. IGMP snooping + querier on the AES67 VLAN.
 
 ## Syslog