Phase 5: Lightning auto-payout with LNURL-pay and NUT-05 melt

- New lnurl_pay.c/h: LNURL-pay protocol (GET .well-known/lnurlp + callback)
- New lightning_payout.c/h: threshold-based auto-payout with multi-recipient split
- Extended nucula_wallet bridge with nucula_wallet_melt() (NUT-05)
- Config: payout section with multi-mint, multi-recipient, fee_tolerance
- Default: enabled, TollGate@coinos.io, min_payout=128, min_balance=64
- 18 new unit tests (all passing), 134 total

1 files changed, 97 insertions, 0 deletions

diff --git a/tests/unit/test_lightning_payout.c b/tests/unit/test_lightning_payout.c
new file mode 100644
index 0000000..8501eb9
--- /dev/null
+++ b/tests/unit/test_lightning_payout.c
@@ -0,0 +1,97 @@
+#include "test_framework.h"
+#include "../../main/lightning_payout.h"
+#include "../../main/config.h"
+#include <string.h>
+#include <stdio.h>
+#include <math.h>
+
+static void test_payout_calculation(void)
+{
+    printf("\n--- Payout pool calculation ---\n");
+    {
+        uint64_t balance = 500;
+        uint64_t min_balance = 64;
+        uint64_t min_payout_amount = 128;
+
+        ASSERT(balance >= min_payout_amount, "500 >= 128 triggers payout");
+
+        uint64_t pool = balance - min_balance;
+        ASSERT_EQ_INT(436, (int)pool, "pool = 500 - 64 = 436");
+    }
+
+    printf("\n--- Payout below threshold ---\n");
+    {
+        uint64_t balance = 100;
+        uint64_t min_payout_amount = 128;
+
+        ASSERT(balance < min_payout_amount, "100 < 128, no payout");
+    }
+
+    printf("\n--- Multi-recipient split ---\n");
+    {
+        uint64_t pool = 436;
+        double factors[] = {0.79, 0.21};
+        const char *names[] = {"owner", "developer"};
+
+        uint64_t total = 0;
+        for (int i = 0; i < 2; i++) {
+            uint64_t share = (uint64_t)round((double)pool * factors[i]);
+            printf("  %s: factor=%.2f share=%llu\n", names[i], factors[i], (unsigned long long)share);
+            total += share;
+        }
+        ASSERT_EQ_INT(436, (int)total, "79/21 split sums to pool");
+    }
+
+    printf("\n--- Single recipient 100%% ---\n");
+    {
+        uint64_t pool = 436;
+        double factor = 1.0;
+        uint64_t share = (uint64_t)round((double)pool * factor);
+        ASSERT_EQ_INT(436, (int)share, "1.0 factor = full pool");
+    }
+
+    printf("\n--- Fee tolerance calculation ---\n");
+    {
+        uint64_t share = 344;
+        uint64_t fee_pct = 10;
+        uint64_t max_cost = share + (share * fee_pct / 100);
+        ASSERT_EQ_INT(378, (int)max_cost, "344 + 10% = 378");
+    }
+
+    printf("\n--- Zero pool (balance == reserve) ---\n");
+    {
+        uint64_t balance = 64;
+        uint64_t min_balance = 64;
+        uint64_t pool = balance - min_balance;
+        ASSERT_EQ_INT(0, (int)pool, "no payout when balance == reserve");
+    }
+
+    printf("\n--- Payout config defaults ---\n");
+    {
+        payout_config_t cfg;
+        memset(&cfg, 0, sizeof(cfg));
+        cfg.enabled = true;
+        cfg.mint_count = 1;
+        strncpy(cfg.mints[0].url, "https://testnut.cashu.space", sizeof(cfg.mints[0].url) - 1);
+        cfg.mints[0].min_balance = 64;
+        cfg.mints[0].min_payout_amount = 128;
+        cfg.recipient_count = 1;
+        strncpy(cfg.recipients[0].lightning_address, "TollGate@coinos.io",
+                sizeof(cfg.recipients[0].lightning_address) - 1);
+        cfg.recipients[0].factor = 1.0;
+        cfg.fee_tolerance_pct = 10;
+        cfg.check_interval_s = 60;
+
+        ASSERT(cfg.enabled, "payout enabled");
+        ASSERT_EQ_INT(1, cfg.mint_count, "1 mint");
+        ASSERT_EQ_INT(1, cfg.recipient_count, "1 recipient");
+        ASSERT_EQ_STR("TollGate@coinos.io", cfg.recipients[0].lightning_address, "default LNURL");
+    }
+}
+
+int main(void)
+{
+    printf("=== test_lightning_payout ===\n");
+    test_payout_calculation();
+    TEST_SUMMARY();
+}