Complete Phase 12 dual-stack networking

Add IPv6-aware Wi-Fi state, HTTPS/SSH listeners, mDNS service
reconciliation, and browser Wi-Fi administration.

Include a guarded build-local fix for mDNS 1.12.0 membership handling,
focused regression suites, and Phase 12 acceptance documentation.

src/web_server.c

@@ -40,6 +40,7 @@
 #include "web_diagnostics.h"
 #include "web_ui.h"
 #include "wifi_manager.h"
+#include "mdns_service.h"
 
 #define WEB_SERVER_PORT 443U
 #define WEB_SERVER_STATUS_JSON_CAPACITY 3072U
@@ -271,7 +272,7 @@ static esp_err_t status_handler(httpd_req_t *request)
         "{\n"
         "  \"uptime_ms\":%" PRIu64 ",\n"
         "  \"wifi\":{\"available\":%s,\"state\":\"%s\",\"sta_ipv4\":\"%s\","
-        "\"rssi\":%d,\"channel\":%u,\"ap_running\":%s,\"ap_clients\":%u},\n"
+        "\"ipv6_linklocal\":%s,\"ipv6_routable\":%s,\"rssi\":%d,\"channel\":%u,\"ap_running\":%s,\"ap_clients\":%u},\n"
         "  \"serial\":{\"running\":%s,\"config_available\":%s,\"baud\":%" PRIu32 ","
         "\"data_bits\":\"%s\",\"parity\":\"%s\",\"stop_bits\":\"%s\","
         "\"flow\":\"%s\",\"rx_bytes\":%" PRIu64 ",\"rx_dropped\":%" PRIu64 ","
@@ -289,7 +290,10 @@ static esp_err_t status_handler(httpd_req_t *request)
         (uint64_t)(esp_timer_get_time() / 1000),
         wifi_available ? "true" : "false",
         wifi_available ? wifi_manager_state_to_string(wifi.state) : "unavailable",
-        ipv4, wifi_available ? (int)wifi.sta_rssi : 0,
+        ipv4,
+                wifi_available && wifi.ipv6_linklocal ? "true" : "false",
+                wifi_available && wifi.ipv6_routable ? "true" : "false",
+                wifi_available ? (int)wifi.sta_rssi : 0,
         wifi_available ? (unsigned int)wifi.sta_channel : 0U,
         wifi_available && wifi.ap_running ? "true" : "false",
         wifi_available ? (unsigned int)wifi.ap_client_count : 0U,
@@ -786,6 +790,7 @@ static esp_err_t start_server(bool reserved)
     s_serial_transport_error = attach_error;
     s_serial_transport_attached = serial_transport_attached;
     s_admin_transport_owned = admin_transport_owned;
+    mdns_service_set_https_available(error == ESP_OK);
     if (error == ESP_OK) {
         s_server = server;
         ++s_counters.starts;
@@ -824,6 +829,8 @@ static esp_err_t stop_server(uint32_t expected_generation, bool restart, bool re
     esp_err_t serial_transport_error = s_serial_transport_error;
     s_transitioning = true;
     if (s_generation != UINT32_MAX) ++s_generation;
+    /* Admission is about to close, even if later teardown must be retried. */
+    mdns_service_set_https_available(false);
     xSemaphoreGive(s_server_mutex);
 
     web_cookie_auth_stop();