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, 68 insertions, 0 deletions

diff --git a/tollgate_core/include/tollgate_platform.h b/tollgate_core/include/tollgate_platform.h
new file mode 100644
index 0000000..b553a83
--- /dev/null
+++ b/tollgate_core/include/tollgate_platform.h
@@ -0,0 +1,68 @@
+#ifndef TOLLGATE_PLATFORM_H
+#define TOLLGATE_PLATFORM_H
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stddef.h>
+
+typedef struct {
+    uint16_t     (*get_price_sats)(void);
+    int32_t      (*get_step_ms)(void);
+    int64_t      (*get_step_bytes)(void);
+    const char*  (*get_mint_url)(void);
+    const char*  (*get_metric)(void);
+
+    int64_t      (*get_time_ms)(void);
+
+    void         (*log_info)(const char *tag, const char *fmt, ...);
+    void         (*log_warn)(const char *tag, const char *fmt, ...);
+    void         (*log_error)(const char *tag, const char *fmt, ...);
+
+    bool         (*wallet_receive)(const char *token);
+    bool         (*wallet_send)(uint64_t amount, char *buf, size_t buf_len);
+    uint64_t     (*wallet_balance)(void);
+
+    int          (*http_post)(const char *url, const char *headers,
+                             const char *body, int body_len,
+                             char *resp, int resp_len);
+
+    bool         (*create_task)(void (*fn)(void*), void *arg,
+                               const char *name, int stack_bytes, int priority);
+
+    int          (*socket_udp)(void);
+    int          (*socket_tcp)(void);
+    int          (*socket_bind)(int fd, uint32_t ip, uint16_t port);
+    int          (*socket_listen)(int fd, int backlog);
+    int          (*socket_accept)(int fd, uint32_t *client_ip, uint16_t *client_port);
+    int          (*socket_recvfrom)(int fd, void *buf, int len,
+                                    uint32_t *src_ip, uint16_t *src_port);
+    int          (*socket_sendto)(int fd, const void *buf, int len,
+                                  uint32_t dest_ip, uint16_t dest_port);
+    int          (*socket_read)(int fd, void *buf, int len);
+    int          (*socket_write)(int fd, const void *buf, int len);
+    void         (*socket_close)(int fd);
+    void         (*socket_set_recv_timeout)(int fd, int ms);
+
+    bool         (*get_sta_mac_ip_list)(void *list_out, int max, int *count_out);
+    bool         (*set_vendor_ie)(bool enable, const void *ie_data, int ie_len);
+    int          (*arp_get_mac)(uint32_t ip, uint8_t *mac_out);
+    void         (*napt_enable)(uint32_t ip, bool enable);
+
+    bool         (*mining_enabled)(void);
+    const char*  (*get_stratum_host)(void);
+    uint16_t     (*get_stratum_port)(void);
+    const char*  (*get_stratum_user)(void);
+    const char*  (*get_stratum_pass)(void);
+    uint16_t     (*get_mining_port)(void);
+    uint64_t     (*get_hashprice_override)(void);
+
+    void         (*fill_random)(void *buf, int len);
+
+    int          (*get_accepted_mint_count)(void);
+    const char*  (*get_accepted_mint)(int index);
+    bool         (*is_mint_reachable)(const char *mint_url);
+    bool         (*mac_for_ip)(uint32_t ip, char *mac_out, int mac_out_size);
+
+} tollgate_platform_t;
+
+#endif