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/wifi_manager.h

@@ -42,6 +42,14 @@ typedef struct {
     uint64_t queue_drops;
 } wifi_manager_counters_t;
 
+#define WIFI_MANAGER_IPV6_MAX_ADDRESSES 3U
+
+/* Network-order words, compatible with IDF's IPV62STR/ESP_IP6_ADDR_BLOCK macros.
+ * No device-local zone: a remote client must select its own interface. */
+typedef struct {
+    uint32_t addr[4];
+} wifi_manager_ipv6_address_t;
+
 typedef struct {
     bool initialized;
     bool started;
@@ -54,6 +62,13 @@ typedef struct {
     uint32_t ip;
     uint32_t netmask;
     uint32_t gateway;
+    /* Preferred IPv6 addresses only (DAD complete, not deprecated/expired).
+     * ONLINE means IPv4 or either IPv6 flag, not Internet reachability.
+     * routable includes ULA/GUA; it does not assert a default route exists. */
+    bool ipv6_linklocal;
+    bool ipv6_routable;
+    uint8_t ipv6_count;
+    wifi_manager_ipv6_address_t ipv6_addresses[WIFI_MANAGER_IPV6_MAX_ADDRESSES];
     uint8_t sta_channel;
     int8_t sta_rssi;
     wifi_auth_mode_t sta_auth;
@@ -141,7 +156,10 @@ esp_err_t wifi_manager_stop(void);
 esp_err_t wifi_manager_reconnect(void);
 /* Advance to the next enabled station profile in priority order, wrapping safely. */
 esp_err_t wifi_manager_next_profile(void);
-/* Reannounce the configured hostname when the manager currently has a STA IP. */
+/* Refresh DHCPv4 option 12 from the configured sak-<suffix> hostname, and
+ * reannounce mDNS when ONLINE (either IP family). No lease restart: the new
+ * name is used in subsequent DHCP exchanges, including renew/rebind; existing
+ * router/DNS records may remain until server policy expires or replaces them. */
 esp_err_t wifi_manager_mdns_reannounce(void);
 
 /* Snapshot data never contains station or AP passwords. */