feat: extract tollgate_core ESP-IDF component

Extract shared TollGate business logic into a reusable ESP-IDF component
that can be consumed by esp-miner via the IDF Component Manager.

Component structure:
  components/tollgate_core/
    include/tollgate_core.h       — public API
    include/tollgate_platform.h   — platform interface (config callbacks)
    src/tollgate_core.c           — orchestrator (init, payment, tick, owner)
    src/tollgate_core_cashu.c/h   — Cashu V3 token decode/verify
    src/tollgate_core_dns.c/h     — per-client DNS hijack/forward
    src/tollgate_core_firewall.c/h — per-client NAT filter
    src/tollgate_core_session.c/h — session lifecycle

Key design decisions:
  - Platform interface pattern: consumers implement tollgate_platform_t
    (config getters + optional spend_proofs wallet hook)
  - Cross-module wiring (session→firewall→dns) stays internal
  - No direct config.h dependency — all config via platform callbacks
  - spend_proofs can be NULL (accepts payment without local wallet)

Standalone app updated:
  - main/tollgate_platform.c implements platform via config singleton
  - main/tollgate_main.c calls tollgate_core_init/tick/dns_start
  - main/tollgate_api.c routes payment through tollgate_core_process_payment
  - Removed cashu.c, dns_server.c, firewall.c, session.c from CMakeLists

Not yet build-verified — blocked on multi-mint, price-discovery,
cvm-integration, and display-fix branches merging to master.

2 files changed, 51 insertions, 0 deletions

diff --git a/components/tollgate_core/include/tollgate_core.h b/components/tollgate_core/include/tollgate_core.h
new file mode 100644
index 0000000..c47ebeb
--- /dev/null
+++ b/components/tollgate_core/include/tollgate_core.h
@@ -0,0 +1,34 @@
+#ifndef TOLLGATE_CORE_H
+#define TOLLGATE_CORE_H
+
+#include "tollgate_platform.h"
+#include "esp_err.h"
+#include "esp_netif.h"
+#include <stdbool.h>
+#include <stdint.h>
+
+esp_err_t tollgate_core_init(const tollgate_platform_t *platform, esp_ip4_addr_t ap_ip);
+
+esp_err_t tollgate_core_dns_start(esp_ip4_addr_t upstream_dns);
+void tollgate_core_dns_stop(void);
+
+esp_err_t tollgate_core_process_payment(uint32_t client_ip, const char *token_str);
+
+void tollgate_core_client_connected(const uint8_t *mac, uint32_t client_ip);
+void tollgate_core_client_disconnected(const uint8_t *mac);
+
+void tollgate_core_tick(void);
+
+bool tollgate_core_is_client_allowed(uint32_t client_ip);
+bool tollgate_core_is_dns_running(void);
+
+char *tollgate_core_get_status_json(void);
+char *tollgate_core_get_config_json(void);
+
+int tollgate_core_active_session_count(void);
+int tollgate_core_allowed_client_count(void);
+
+bool tollgate_core_is_owner(uint32_t client_ip);
+bool tollgate_core_is_owner_connected(void);
+
+#endif
diff --git a/components/tollgate_core/include/tollgate_platform.h b/components/tollgate_core/include/tollgate_platform.h
new file mode 100644
index 0000000..f60f1f9
--- /dev/null
+++ b/components/tollgate_core/include/tollgate_platform.h
@@ -0,0 +1,17 @@
+#ifndef TOLLGATE_PLATFORM_H
+#define TOLLGATE_PLATFORM_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+typedef struct {
+    uint16_t     (*get_price_sats)(void);
+    int32_t      (*get_step_ms)(void);
+    const char * (*get_mint_url)(void);
+    const char * (*get_metric)(void);
+    int32_t      (*get_step_bytes)(void);
+    int64_t      (*get_time_ms)(void);
+    bool         (*spend_proofs)(const char *raw_token_json);
+} tollgate_platform_t;
+
+#endif