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, 125 insertions, 0 deletions

diff --git a/tests/unit/test_stratum_client.c b/tests/unit/test_stratum_client.c
new file mode 100644
index 0000000..302fcba
--- /dev/null
+++ b/tests/unit/test_stratum_client.c
@@ -0,0 +1,125 @@
+#include "test_framework.h"
+#include "../../components/tollgate_core/src/tollgate_core_stratum_client.h"
+#include <cjson/cJSON.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(void)
+{
+    printf("=== test_stratum_client ===\n");
+
+    printf("\n--- hex_to_bytes ---\n");
+    {
+        const char *hex = "0a1b2c3d";
+        uint8_t out[4] = {0};
+        tollgate_core_stratum_hex_to_bytes(hex, out, 4);
+        ASSERT_EQ_INT(0x0a, (int)out[0], "byte 0");
+        ASSERT_EQ_INT(0x1b, (int)out[1], "byte 1");
+        ASSERT_EQ_INT(0x2c, (int)out[2], "byte 2");
+        ASSERT_EQ_INT(0x3d, (int)out[3], "byte 3");
+    }
+
+    printf("\n--- hex_to_bytes zeros ---\n");
+    {
+        const char *hex = "00000000";
+        uint8_t out[4] = {0xff, 0xff, 0xff, 0xff};
+        tollgate_core_stratum_hex_to_bytes(hex, out, 4);
+        ASSERT_EQ_INT(0, (int)out[0], "zero byte 0");
+        ASSERT_EQ_INT(0, (int)out[1], "zero byte 1");
+    }
+
+    printf("\n--- parse_notify valid ---\n");
+    {
+        cJSON *params = cJSON_Parse("[\"123\",\"0000000000000000000000000000000000000000000000000000000000000000\","
+                                     "\"\""
+                                     ",\"\""
+                                     ",\"\""
+                                     ",\"20000000\""
+                                     ",\"1705e3c4\""
+                                     ",\"65a3b2c1\"]");
+        tollgate_stratum_job_t job = {0};
+        uint32_t nbits = 0;
+        bool ok = tollgate_core_stratum_parse_notify(params, &job, &nbits);
+        ASSERT(ok, "parse_notify returns true");
+        ASSERT_EQ_INT(123, (int)job.job_id, "job_id parsed");
+        ASSERT(job.valid, "job is valid");
+        ASSERT_EQ_INT(0x20000000, (int)job.version, "version parsed");
+        ASSERT_EQ_INT(0x1705e3c4, (int)job.nbits, "nbits parsed");
+        ASSERT_EQ_INT(0x65a3b2c1, (int)job.ntime, "ntime parsed");
+        ASSERT_EQ_INT(0x1705e3c4, (int)nbits, "out_nbits set");
+        ASSERT_EQ_INT(32, job.target_len, "target_len is 32");
+        cJSON_Delete(params);
+    }
+
+    printf("\n--- parse_notify too few params ---\n");
+    {
+        cJSON *params = cJSON_Parse("[\"123\",\"abcd\"]");
+        tollgate_stratum_job_t job = {0};
+        bool ok = tollgate_core_stratum_parse_notify(params, &job, NULL);
+        ASSERT(!ok, "parse_notify returns false for insufficient params");
+        cJSON_Delete(params);
+    }
+
+    printf("\n--- parse_notify NULL ---\n");
+    {
+        tollgate_stratum_job_t job = {0};
+        bool ok = tollgate_core_stratum_parse_notify(NULL, &job, NULL);
+        ASSERT(!ok, "parse_notify returns false for NULL");
+    }
+
+    printf("\n--- parse_difficulty valid ---\n");
+    {
+        cJSON *params = cJSON_Parse("[512]");
+        uint64_t diff = 0;
+        bool ok = tollgate_core_stratum_parse_difficulty(params, &diff);
+        ASSERT(ok, "parse_difficulty returns true");
+        ASSERT_EQ_UINT64(512, (unsigned long long)diff, "difficulty parsed");
+        cJSON_Delete(params);
+    }
+
+    printf("\n--- parse_difficulty invalid ---\n");
+    {
+        cJSON *params = cJSON_Parse("[]");
+        uint64_t diff = 0;
+        bool ok = tollgate_core_stratum_parse_difficulty(params, &diff);
+        ASSERT(!ok, "parse_difficulty returns false for empty array");
+        cJSON_Delete(params);
+    }
+
+    printf("\n--- build_subscribe ---\n");
+    {
+        char buf[256];
+        int len = tollgate_core_stratum_build_subscribe(buf, sizeof(buf), 1);
+        ASSERT(len > 0, "build_subscribe returns positive length");
+        ASSERT(strstr(buf, "mining.subscribe") != NULL, "contains method");
+        ASSERT(strstr(buf, "\"id\":1") != NULL, "contains id");
+        ASSERT(strstr(buf, "TollGate/1.0") != NULL, "contains user agent");
+        ASSERT(buf[len - 1] == '\n', "ends with newline");
+    }
+
+    printf("\n--- build_authorize ---\n");
+    {
+        char buf[512];
+        int len = tollgate_core_stratum_build_authorize(buf, sizeof(buf), 2, "user1", "pass1");
+        ASSERT(len > 0, "build_authorize returns positive length");
+        ASSERT(strstr(buf, "mining.authorize") != NULL, "contains method");
+        ASSERT(strstr(buf, "user1") != NULL, "contains user");
+        ASSERT(strstr(buf, "pass1") != NULL, "contains pass");
+    }
+
+    printf("\n--- build_submit ---\n");
+    {
+        char buf[512];
+        int len = tollgate_core_stratum_build_submit(buf, sizeof(buf), 3, "worker1",
+                                                       100, 0x65a3b2c1, 0x12345678, 0x20000000);
+        ASSERT(len > 0, "build_submit returns positive length");
+        ASSERT(strstr(buf, "mining.submit") != NULL, "contains method");
+        ASSERT(strstr(buf, "worker1") != NULL, "contains worker");
+        ASSERT(strstr(buf, "100") != NULL, "contains job_id");
+        ASSERT(strstr(buf, "65a3b2c1") != NULL, "contains ntime");
+        ASSERT(strstr(buf, "12345678") != NULL, "contains nonce");
+    }
+
+    TEST_SUMMARY();
+}