Step 5 (SAP): announce the stream via SAP

- aes67_sdp_sap: SAP (RFC 2974) announcer task. SAPv1 to
  239.255.255.255:9875 every 30 s and within 1 s of any SDP change
  (config save, GM change), with the old hash deleted first. Active while
  aes67.discovery = sap, the stream is enabled, the AES67 interface has
  an IP and a PTP GM is known. Deletion when that stops and at shutdown
  (reboot/OTA) via a shutdown handler. TTL = aes67.ttl.
- Docs: SAP implementation notes; session_ver bump on GM change still open.
- Verified with a SAP listener: 30 s repeats with a stable hash; rename
  -> delete old + announce new (o= version follows); manual -> delete;
  sap -> announce; reboot and OTA -> delete at shutdown, first announce
  after boot only once the GM is known.

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

components/aes67_sdp_sap/CMakeLists.txt

@@ -1,3 +1,3 @@
 idf_component_register(SRCS "aes67_sdp_sap.c"
                        INCLUDE_DIRS "include"
-                       PRIV_REQUIRES aes67_net aes67_ptp aes67_web esp_netif)
+                       PRIV_REQUIRES aes67_net aes67_ptp aes67_web esp_netif esp_timer lwip)