Phase 4: TollGate client detection + auto-payment

- New tollgate_client.c/h: detect upstream TollGate (kind=10021),
  auto-pay via nucula wallet, session monitoring with 20% renewal
- State machine: IDLE→DETECTING→NEEDS_PAY→PAYING→PAID→RENEWING
- Blocking: upstream payment before local services start
- Synchronous wallet init (was async task)
- Client config: enabled, steps_to_buy, renewal_threshold_pct
- Updated PLAN.md with Phases 4-7 (client, payout, bytes, CVM)
- Updated CHECKLIST.md with all new phase items
- 30 new unit tests (all passing), 116 total

1 files changed, 1 insertions, 0 deletions

diff --git a/tests/unit/stubs/esp_err.h b/tests/unit/stubs/esp_err.h
index 9bedb72..2a8e216 100644
--- a/tests/unit/stubs/esp_err.h
+++ b/tests/unit/stubs/esp_err.h
@@ -12,6 +12,7 @@ typedef int esp_err_t;
 #define ESP_ERR_INVALID_ARG  0x102
 #define ESP_ERR_NO_MEM       0x101
 #define ESP_ERR_NOT_FOUND    0x104
+#define ESP_ERR_INVALID_STATE 0x103
 
 static inline const char *esp_err_to_name(esp_err_t err) { (void)err; return "ESP_OK"; }