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, 5 insertions, 8 deletions

diff --git a/tests/unit/Makefile b/tests/unit/Makefile
index 7bd3f1e..a06807f 100644
--- a/tests/unit/Makefile
+++ b/tests/unit/Makefile
@@ -22,7 +22,7 @@ LDFLAGS := -lmbedcrypto -lcjson -lm
 
 SECP256K1_OBJ := secp256k1.o precomputed_ecmult.o precomputed_ecmult_gen.o
 
-TESTS := test_geohash test_identity test_nostr_event test_cashu test_session test_tollgate_client test_lnurl_pay test_lightning_payout test_mcp_handler test_nip04 test_cvm_server test_display test_negentropy_adapter test_beacon_price test_market
+TESTS := test_geohash test_identity test_nostr_event test_cashu test_session test_tollgate_client test_lnurl_pay test_lightning_payout test_mcp_handler test_nip04 test_cvm_server test_display test_negentropy_adapter test_beacon_price test_market test_mint_health
 
 .PHONY: all test clean $(TESTS)
 
@@ -58,10 +58,10 @@ test_nostr_event: test_nostr_event.c $(REPO_ROOT)/main/nostr_event.c $(REPO_ROOT
         $(CC) $(CFLAGS) -I $(SECP256K1_PRIV_INC) $< $(REPO_ROOT)/main/nostr_event.c $(REPO_ROOT)/main/identity.c $(SECP256K1_OBJ) -o $@ $(LDFLAGS)
 
 test_cashu: test_cashu.c $(REPO_ROOT)/main/cashu.c
-        $(CC) $(CFLAGS) $< $(REPO_ROOT)/main/cashu.c -o $@ $(LDFLAGS)
+        $(CC) $(CFLAGS) -include stubs/mint_health.h $< $(REPO_ROOT)/main/cashu.c -o $@ $(LDFLAGS)
 
 test_session: test_session.c $(REPO_ROOT)/main/session.c $(REPO_ROOT)/main/cashu.c
-        $(CC) $(CFLAGS) $< $(REPO_ROOT)/main/session.c $(REPO_ROOT)/main/cashu.c -o $@ $(LDFLAGS)
+        $(CC) $(CFLAGS) -include stubs/mint_health.h $< $(REPO_ROOT)/main/session.c $(REPO_ROOT)/main/cashu.c -o $@ $(LDFLAGS)
 
 test_tollgate_client: test_tollgate_client.c $(REPO_ROOT)/main/market.c $(REPO_ROOT)/main/beacon_price.c
         $(CC) $(CFLAGS) -I $(REPO_ROOT)/main $< $(REPO_ROOT)/main/market.c $(REPO_ROOT)/main/beacon_price.c -o $@ $(LDFLAGS)
@@ -81,11 +81,8 @@ test_nip04: test_nip04.c $(REPO_ROOT)/main/nip04.c $(SECP256K1_OBJ)
 test_cvm_server: test_cvm_server.c
         $(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
 
-test_display: test_display.c
-        $(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
-
-test_negentropy_adapter: test_negentropy_adapter.c
-        $(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
+test_mint_health: test_mint_health.c $(REPO_ROOT)/main/mint_health.c
+        $(CC) -Wall -Wextra -Wno-unused-parameter -Wno-unused-function -Wno-sign-compare -std=gnu17 -g -O0 -DTEST_HOST -include stubs/esp_err.h -I $(REPO_ROOT)/main -I stubs -I $(SECP256K1_INC) -I $(SECP256K1_CFG) -I /usr/include/cjson $< $(REPO_ROOT)/main/mint_health.c -o $@ $(LDFLAGS)
 
 test_beacon_price: test_beacon_price.c $(REPO_ROOT)/main/beacon_price.c
         $(CC) $(CFLAGS) -I $(REPO_ROOT)/main $< $(REPO_ROOT)/main/beacon_price.c -o $@ $(LDFLAGS)