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, 5 insertions, 0 deletions

diff --git a/main/config.h b/main/config.h
index 8254a62..4c6116e 100644
--- a/main/config.h
+++ b/main/config.h
@@ -49,6 +49,11 @@ typedef struct {
     int nostr_publish_interval_s;
 
     bool identity_initialized;
+
+    bool client_enabled;
+    int client_steps_to_buy;
+    int client_renewal_threshold_pct;
+    int client_retry_interval_ms;
 } tollgate_config_t;
 
 void tollgate_config_derive_unique(tollgate_config_t *cfg);