Step 4.1: /stream.sdp from the live config and PTP GM

- aes67_sdp_sap: aes67_sdp_build() builds the AES67 SDP (RFC 4566 +
  RFC 7273) with the same lines and order as the web UI preview;
  GET /stream.sdp serves it as application/sdp.
- aes67_ptp: public aes67_ptp_gm_id(), aes67_ptp_locked(),
  aes67_ptp_now_ns(). Clock IDs are now uppercase (RFC 7273 style), also
  in status.ptp, which the UI copies into ts-refclk.
- aes67_net: aes67_net_netif() returns the AES67 interface.
- Verified on board: /stream.sdp byte-identical to the UI's sdp() for
  the same config/status; mono, L16, ptime 0.333, ttl 8, clk_offset
  4294967295 and session_ver all follow the config.

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

components/aes67_ptp/ptp_clock.c

@@ -150,7 +150,7 @@ static int64_t mac_ns(const eth_mac_time_t *t)
 
 static void fmt_id(char *out, const uint8_t *id)
 {
-    sprintf(out, "%02x-%02x-%02x-%02x-%02x-%02x-%02x-%02x", id[0], id[1], id[2], id[3], id[4], id[5], id[6], id[7]);
+    sprintf(out, "%02X-%02X-%02X-%02X-%02X-%02X-%02X-%02X", id[0], id[1], id[2], id[3], id[4], id[5], id[6], id[7]);
 }
 
 // IEEE 1588 dataset comparison (without the topology part): <0 if a is better.
@@ -487,6 +487,22 @@ static void ptp_task(void *arg)
     }
 }
 
+bool ptp_clock_gm_id(char out[24])
+{
+    xSemaphoreTake(s.lock, portMAX_DELAY);
+    bool valid = s.gm.valid;
+    if (valid) {
+        fmt_id(out, s.gm.gm_id);
+    }
+    xSemaphoreGive(s.lock);
+    return valid;
+}
+
+bool ptp_clock_locked(void)
+{
+    return s.locked;
+}
+
 void ptp_clock_status(cJSON *st)
 {
     cJSON *p = cJSON_AddObjectToObject(st, "ptp");