feat: multi-mint health tracker, discovery, portal, multi-wallet (Phase 3-8)

- mint_health.h/c: FreeRTOS probing task, GET /v1/info every 5min,
  recovery threshold 3, immediate failure, mutex-protected state
- cashu.c: health-gated acceptance (config match AND reachable)
- tollgate_api.c: one price_per_step tag per reachable mint in discovery
- captive_portal.c: mint list with green/grey indicators, /mints API,
  auto-refresh every 30s via JS
- nucula_wallet.h/cpp: multi-wallet (up to 4), route receive to correct
  wallet by mint URL, balance sums across all wallets
- tollgate_main.c: init health tracker + multi-wallet on service start
- CMakeLists.txt: add mint_health.c

1 files changed, 3 insertions, 2 deletions

diff --git a/main/CMakeLists.txt b/main/CMakeLists.txt
index 9b0fb1c..1416e07 100644
--- a/main/CMakeLists.txt
+++ b/main/CMakeLists.txt
@@ -15,8 +15,9 @@ idf_component_register(SRCS "tollgate_main.c"
                             "lightning_payout.c"
                             "nip04.c"
                             "mcp_handler.c"
-                            "cvm_server.c"
-                            "display.c"
+                             "cvm_server.c"
+                             "mint_health.c"
+                             "display.c"
                             "font.c"
                     INCLUDE_DIRS "."
                     REQUIRES esp_wifi esp_event esp_netif nvs_flash esp_http_server