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>

components/aes67_net/CMakeLists.txt

@@ -1,4 +1,4 @@
 idf_component_register(SRCS "aes67_net.c"
                        INCLUDE_DIRS "include"
                        REQUIRES esp_eth esp_netif esp_event
-                       PRIV_REQUIRES aes67_web lwip)
+                       PRIV_REQUIRES aes67_web lwip espressif__mdns)