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_health/aes67_health.c

@@ -1,7 +1,19 @@
 #include "aes67_health.h"
 
-// Stub (build step 0).
+#include "aes67_web.h"
+#include "esp_app_desc.h"
+#include "esp_heap_caps.h"
+#include "esp_timer.h"
+
+static void health_status(cJSON *st)
+{
+    cJSON_AddStringToObject(st, "fw", esp_app_get_description()->version);
+    cJSON_AddNumberToObject(st, "uptime_s", (double)(esp_timer_get_time() / 1000000));
+    cJSON_AddNumberToObject(st, "heap_free", heap_caps_get_free_size(MALLOC_CAP_INTERNAL));
+    cJSON_AddNumberToObject(st, "psram_free", heap_caps_get_free_size(MALLOC_CAP_SPIRAM));
+}
+
 esp_err_t aes67_health_init(void)
 {
-    return ESP_OK;
+    return status_register(health_status);
 }