Phase 8c-8f: Extract portal, stratum_client, mint_health, client into tollgate_core

New component modules:
- tollgate_core_portal.c/h: template rendering, usage calc, captive URI detection
- tollgate_core_stratum_client.c/h: Stratum V1 JSON protocol parsing, message building
- tollgate_core_mint_health.c/h: mint health state tracking, recovery threshold logic
- tollgate_core_client.c/h: discovery/session/usage JSON parsing, renewal check, price calc

Main shims updated to delegate pure logic to component:
- captive_portal.c: uses tollgate_core_portal_render(), format_usage(), is_captive_uri()
- stratum_client.c: uses tollgate_core_stratum_parse_notify/build_*()
- mint_health.c: uses tollgate_core_mint_health_update/is_reachable/mark_unreachable()
- tollgate_client.c: uses tollgate_core_client_parse_*/should_renew/calc_price_per_min()

4 new unit tests (test_portal, test_stratum_client, test_mint_health_core, test_client_core)
All 25 unit tests pass. ESP-IDF build passes (68% partition free).

1 files changed, 1 insertions, 26 deletions

diff --git a/main/tollgate_client.h b/main/tollgate_client.h
index ccee624..463cf63 100644
--- a/main/tollgate_client.h
+++ b/main/tollgate_client.h
@@ -1,36 +1,11 @@
 #ifndef TOLLGATE_CLIENT_H
 #define TOLLGATE_CLIENT_H
 
+#include "tollgate_core_client.h"
 #include "esp_err.h"
 #include <stdint.h>
 #include <stdbool.h>
 
-#define TG_CLIENT_MAX_GW_IP_LEN       16
-#define TG_CLIENT_MAX_MINT_URL        256
-#define TG_CLIENT_MAX_METRIC          32
-
-typedef enum {
-    TG_CLIENT_IDLE,
-    TG_CLIENT_DETECTING,
-    TG_CLIENT_NO_TOLLGATE,
-    TG_CLIENT_NEEDS_PAY,
-    TG_CLIENT_PAYING,
-    TG_CLIENT_PAID,
-    TG_CLIENT_RENEWING,
-    TG_CLIENT_MINING,
-    TG_CLIENT_ERROR
-} tollgate_client_state_t;
-
-typedef struct {
-    bool is_tollgate;
-    int price_per_step;
-    int step_size_ms;
-    char mint_url[TG_CLIENT_MAX_MINT_URL];
-    char metric[TG_CLIENT_MAX_METRIC];
-    bool mining_available;
-    uint16_t mining_port;
-} tollgate_discovery_t;
-
 esp_err_t tollgate_client_init(void);
 
 esp_err_t tollgate_client_on_sta_connected(const char *gw_ip_str);