feat: WPA auto-detect, STA connectivity fix, lwip crash fix

- Add wifi_auth_mode config field (WPA2/WPA3) parsed from config.json
- Default to WPA2 (accepts both WPA2 and WPA3 networks)
- Replace hardcoded WIFI_AUTH_WPA3_PSK with runtime threshold mapping
- Reduce MINT_HEALTH_PROBE_INTERVAL_S from 300 to 30 for testing
- Add 3s delay before service start + 5s DNS stabilization for health probes
- Fixes lwip mem_free crash caused by concurrent HTTP at boot

Verified on hardware:
- STA connects to WPA2 home router (Got IP:192.168.2.16)
- All 4 mint health probes complete successfully
- API endpoints return correct data with reachable mint filtering
- 4/4 wallets initialized with real keysets from live mints

1 files changed, 2 insertions, 0 deletions

diff --git a/main/config.h b/main/config.h
index 8e12878..1a32cc2 100644
--- a/main/config.h
+++ b/main/config.h
@@ -65,6 +65,8 @@ typedef struct {
 
     bool cvm_enabled;
     char cvm_relays[256];
+
+    char wifi_auth_mode[16];
 } tollgate_config_t;
 
 void tollgate_config_derive_unique(tollgate_config_t *cfg);