feat: create tollgate_core standalone C library + tollgate_esp IDF component

Phase 1-4: Extract core business logic into reusable library

tollgate_core/ — standalone C library (zero ESP-IDF deps):
  - tollgate_core.c — orchestrator (init, process_payment, process_share, tick)
  - tollgate_cashu.c — V3 token decode, checkstate via platform callback, allotment math
  - tollgate_session.c — session lifecycle state machine (create/find/revoke/extend)
  - tollgate_firewall.c — client allowlist, NAT filter, packet filter
  - tollgate_mining.c — hashprice, nbits→difficulty, shares-to-allotment, client stats

components/tollgate_esp/ — ESP-IDF component wrapper:
  - tollgate_esp_platform.c — implements tollgate_platform_t using ESP-IDF APIs
  - CMakeLists.txt — compiles tollgate_core + ESP wrapper, links to ESP-IDF
  - idf_component.yml — for IDF Component Registry

Platform interface (tollgate_platform.h):
  - Config access: price, step_size, mint_url, metric
  - Time: get_time_ms (via FreeRTOS ticks on ESP)
  - Logging: log_info/warn/error (via ESP_LOG on ESP)
  - Wallet: receive/send/balance (via nucula on ESP)
  - HTTP: http_post (via esp_http_client on ESP)
  - WiFi/MAC: mac_for_ip, napt_enable
  - Mining: stratum config, hashprice override

Build verification:
  - tollgate_core compiles standalone: cmake + make (gcc, host)
  - tollgate_esp + ESP-IDF full build: passes (idf.py build)
  - Unit tests: 22/22 pass (make test-unit)
  - No behavioral change to existing main/ code yet (Phase 5)

1 files changed, 34 insertions, 0 deletions

diff --git a/tollgate_core/src/tollgate_mining.h b/tollgate_core/src/tollgate_mining.h
new file mode 100644
index 0000000..39681a5
--- /dev/null
+++ b/tollgate_core/src/tollgate_mining.h
@@ -0,0 +1,34 @@
+#ifndef TOLLGATE_CORE_MINING_H
+#define TOLLGATE_CORE_MINING_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#define TG_MINING_SHARE_WINDOW_S 30
+#define TG_MINING_BLOCK_SUBSIDY_SATS 312500000ULL
+#define TG_MINING_BLOCKS_PER_DAY 144ULL
+#define TG_MINING_MAX_CLIENTS 10
+
+typedef struct {
+    uint32_t ip;
+    uint64_t shares_accepted;
+    uint64_t shares_rejected;
+    int64_t first_share_time_ms;
+    int64_t last_share_time_ms;
+    double hashrate_ghs;
+} tg_mining_client_stats_t;
+
+uint64_t tg_mining_nbits_to_difficulty(uint32_t nbits);
+double tg_mining_calculate_hashprice(uint32_t nbits);
+double tg_mining_calculate_hashprice_override(uint64_t sats_per_ghs_day);
+int tg_mining_validate_share(const uint8_t *header80, uint32_t nonce, const uint8_t *target, int target_len);
+uint64_t tg_mining_shares_to_allotment_ms(double hashrate_ghs, double hashprice, int price, int step_ms);
+uint64_t tg_mining_shares_to_allotment_bytes(double hashrate_ghs, double hashprice, int price, int step_bytes);
+tg_mining_client_stats_t *tg_mining_get_or_create_client(uint32_t client_ip);
+void tg_mining_update_hashrate(uint32_t client_ip, bool accepted);
+const tg_mining_client_stats_t *tg_mining_get_client_stats(uint32_t client_ip);
+double tg_mining_get_current_hashprice(void);
+void tg_mining_set_current_nbits(uint32_t nbits);
+void tg_mining_init(void);
+
+#endif