Step 2.1: web server, embedded UI, /api/status, /api/reboot

- aes67_web: httpd (wildcard URI matching), serves web/index.html embedded
  via EMBED_TXTFILES, status registry (status_register) and route registry
  (web_register_uri), GET /api/status, POST /api/reboot (restarts 0.5 s
  after the response).
- Status fields come from each core component: aes67_net (ip, aes67_ip,
  mac, link), aes67_health (fw, uptime_s, heap_free, psram_free),
  aes67_tx stub (tx_packets, underruns = 0). No ptp object yet, so the UI
  shows "no data".
- Verified on board: / serves index.html byte-identical (27601 B),
  /api/status returns live values, reboot via API returns in ~12 s.

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

components/aes67_tx/aes67_tx.c

@@ -1,7 +1,15 @@
 #include "aes67_tx.h"
 
-// Stub (build step 0).
+#include "aes67_web.h"
+
+// Stub (build step 2): counters stay 0 until the RTP sender exists (step 4).
+static void tx_status(cJSON *st)
+{
+    cJSON_AddNumberToObject(st, "tx_packets", 0);
+    cJSON_AddNumberToObject(st, "underruns", 0);
+}
+
 esp_err_t aes67_tx_init(void)
 {
-    return ESP_OK;
+    return status_register(tx_status);
 }