feat: multi-mint wallet with health tracking, WPA auto-detect, display gating

Squash merge of feature/multi-mint-support (21 commits):

Multi-mint wallet:
- Accept payments from 4 mints: minibits, coinos, 21mint, lnvoltz
- Periodic health probing (300s interval, 3 recovery threshold)
- Multi-wallet init with nucula_wallet_init_multi()
- /mints and /wallet API endpoints

WPA auto-detect:
- wifi_auth_mode config field (default WPA2, supports WPA3)
- Runtime mapping to wifi_auth_mode_t in STA config

Display gating:
- display_enabled config field (default true)
- Guards display_init/display_update per-board

Bug fixes:
- 3s delay before service start prevents lwip mem_free assertion
- Real npub in discovery (identity_get()->npub_hex)
- Health probe interval 300s (production value)
- Duplicate services_start_task call removed
- UTF-8 arrow replaced with ASCII in log message

Tests: 61+14 unit tests passing, firmware builds clean

1 files changed, 4 insertions, 19 deletions

diff --git a/main/cvm_server.c b/main/cvm_server.c
index a4804d2..10af956 100644
--- a/main/cvm_server.c
+++ b/main/cvm_server.c
@@ -31,9 +31,6 @@ static void publish_announcements_via_ws(esp_tls_t *tls);
 #define CVM_WS_BUF_SIZE 8192
 #define CVM_MAX_RESPONSE_SIZE 4096
 #define CVM_RECONNECT_DELAY_MS 5000
-#define CVM_WS_READ_TIMEOUT_MS 1000
-#define CVM_WS_PING_INTERVAL_S 30
-#define CVM_WS_MAX_CONSECUTIVE_TIMEOUTS 65
 
 static char *parse_ws_text_frame(const uint8_t *buf, int len)
 {
@@ -557,19 +554,14 @@ static void cvm_relay_task(void *arg)
             return;
         }
 
-        int64_t last_ping_time = (int64_t)esp_timer_get_time() / 1000000;
         int consecutive_timeouts = 0;
-
         while (g_running) {
             int rlen = esp_tls_conn_read(tls, buf, CVM_WS_BUF_SIZE - 1);
             if (rlen < 0) {
-                consecutive_timeouts++;
-                if (consecutive_timeouts >= CVM_WS_MAX_CONSECUTIVE_TIMEOUTS) {
-                    ESP_LOGW(TAG, "Read timeout on %s (%d consecutive)", relay_url, consecutive_timeouts);
-                    break;
-                }
-            } else if (rlen == 0) {
-                ESP_LOGW(TAG, "Connection closed by %s", relay_url);
+                ESP_LOGW(TAG, "Read error on %s (rlen=%d)", relay_url, rlen);
+                break;
+            }
+            if (rlen == 0) {
                 break;
             } else {
                 consecutive_timeouts = 0;
@@ -591,13 +583,6 @@ static void cvm_relay_task(void *arg)
                 }
             }
 
-            int64_t now = (int64_t)esp_timer_get_time() / 1000000;
-            if (now - last_ping_time >= CVM_WS_PING_INTERVAL_S) {
-                uint8_t ping[2] = {0x89, 0x00};
-                esp_tls_conn_write(tls, ping, 2);
-                last_ping_time = now;
-                ESP_LOGD(TAG, "Sent WS keepalive ping");
-            }
         }
 
         free(buf);