feat(mining): Bitcoin mining-for-bandwidth payment system

New modules:
- mining_payment.c/h: hashprice calc (nbits->difficulty->sat/GH/s/day),
  share validation, client stats, allotment conversion (ms + bytes)
- stratum_client.c/h: SV1 upstream pool connection (subscribe/authorize/submit)
- stratum_proxy.c/h: Local SV1 TCP server for downstream miners, job broadcast
- sw_miner.c/h: Software SHA256d miner (ESP32 CPU fallback)
- asic_miner.c/h: ASIC detection stub (BM1366/BM1368 SPI)

Config:
- config.h/c: mining_payout_mode_t enum (auto/pool/upstream/proxy_only),
  stratum pool settings, mining port, hashprice override, sandbox mint access
- Defaults fill nostr_seed_relays (8/8) and nostr_relays (4/4) with fast relays

Integration into existing modules:
- session.h/c: payment_method_t enum (CASHU/MINING/BYTES)
- firewall.h/c: firewall_set_mining_port(), firewall_set_sandbox_mint_access()
- tollgate_api.c: GET /mining/job, POST /mining/share, GET /mining/stats
- tollgate_client.h/c: TG_CLIENT_MINING state, mining discovery tag parsing
- tollgate_main.c: mining init in start_services(), stratum_client_tick() in loop
- captive_portal.c: tabbed Cashu/Mine UI with live hashrate polling

Unit tests (69 new assertions across 4 suites):
- test_mining_payment (23 tests): nbits->difficulty, hashprice, client stats, allotment
- test_stratum_proxy (21 tests): job set/get, stats, type validation
- test_session_payment_method (12 tests): PAYMENT_METHOD enum, bytes/cashu methods
- test_tollgate_client_mining (20 tests): mining tag parsing, discovery struct
- test_firewall_sandbox (16 tests): client grant/revoke, max clients, setters

Enhanced test stubs:
- BaseType_t/pdPASS in freertos/task.h
- lwip: sockets.h, etharp.h, prot/ip.h, prot/ip4.h, prot/tcp.h, netif.h
- dns_server.h, esp_wifi_ap_get_sta_list.h

Build fixes:
- cvm_server.c: replace esp_timer_get_time() with xTaskGetTickCount(),
  fix process_relay_message() 3-arg call to 2-arg, add WS keepalive ping
- stratum_proxy.c: widen task_name buffer 16->20
- sw_miner.c: add missing #include esp_random.h
- nucula_src: save_proofs() moved to public in wallet.hpp

Nostr relay updates:
- nostr_seed_relays: +relay.anzenkodo.workers.dev, +nostr.koning-degraaf.nl,
  +knostr.neutrine.com, +nostr.einundzwanzig.space (8/8 slots)
- nostr_relays: +relay.anzenkodo.workers.dev, +nostr.koning-degraaf.nl (4/4 slots)

Squash-merge of feature/mining-payment (5 commits: c75230e..9d98ba1)

1 files changed, 95 insertions, 0 deletions

diff --git a/tests/unit/test_stratum_proxy.c b/tests/unit/test_stratum_proxy.c
new file mode 100644
index 0000000..7788911
--- /dev/null
+++ b/tests/unit/test_stratum_proxy.c
@@ -0,0 +1,95 @@
+#include "test_framework.h"
+#include "../../main/stratum_proxy.h"
+#include "../../main/mining_payment.h"
+#include <stdio.h>
+#include <string.h>
+
+int main(void)
+{
+    printf("=== test_stratum_proxy ===\n");
+
+    mining_payment_init();
+
+    printf("\n--- stratum_proxy_set_job / get_current_job ---\n");
+    {
+        stratum_job_t job = {0};
+        job.job_id = 42;
+        job.nbits = 0x170309E2;
+        job.ntime = 0x6789ABCD;
+        job.version = 0x20000000;
+        job.valid = true;
+        memset(job.prevhash, 0xAA, 32);
+        memset(job.merkle_root, 0xBB, 32);
+
+        stratum_proxy_set_job(&job);
+
+        const stratum_job_t *cur = stratum_proxy_get_current_job();
+        ASSERT(cur != NULL, "current job not NULL");
+        ASSERT_EQ_INT(42, (int)cur->job_id, "job_id=42");
+        ASSERT_EQ_INT(0x170309E2, (int)cur->nbits, "nbits preserved");
+        ASSERT_EQ_INT(0x6789ABCD, (int)cur->ntime, "ntime preserved");
+        ASSERT_EQ_INT(0x20000000, (int)cur->version, "version preserved");
+        ASSERT(cur->valid, "job is valid");
+        ASSERT_MEM_EQ(job.prevhash, cur->prevhash, 32, "prevhash preserved");
+    }
+
+    printf("\n--- stratum_proxy_set_job (NULL) ---\n");
+    {
+        stratum_proxy_set_job(NULL);
+        const stratum_job_t *cur = stratum_proxy_get_current_job();
+        ASSERT_EQ_INT(42, (int)cur->job_id, "job unchanged after NULL set");
+    }
+
+    printf("\n--- stratum_proxy_get_stats ---\n");
+    {
+        mining_set_current_nbits(0x170309E2);
+        stratum_proxy_set_job(&(stratum_job_t){
+            .job_id = 1,
+            .nbits = 0x170309E2,
+            .valid = true
+        });
+
+        stratum_proxy_stats_t stats;
+        memset(&stats, 0xFF, sizeof(stats));
+        stratum_proxy_get_stats(&stats);
+
+        ASSERT(stats.current_hashprice > 0.0, "hashprice populated from mining_payment");
+        ASSERT_EQ_INT(0x170309E2, (int)stats.nbits, "nbits in stats");
+    }
+
+    printf("\n--- stratum_proxy_get_stats (NULL) ---\n");
+    {
+        stratum_proxy_get_stats(NULL);
+        ASSERT(true, "get_stats with NULL does not crash");
+    }
+
+    printf("\n--- stratum_job_t initialization ---\n");
+    {
+        stratum_job_t zero = {0};
+        ASSERT(!zero.valid, "zero-initialized job is invalid");
+        ASSERT_EQ_INT(0, (int)zero.job_id, "zero job_id");
+        ASSERT_EQ_INT(0, (int)zero.nbits, "zero nbits");
+    }
+
+    printf("\n--- stratum_proxy_stats_t initialization ---\n");
+    {
+        stratum_proxy_stats_t zero = {0};
+        ASSERT(zero.hashrate_ghs == 0.0, "zero hashrate");
+        ASSERT_EQ_INT(0, (int)zero.active_miners, "zero active miners");
+        ASSERT_EQ_UINT64(0, zero.total_shares, "zero total shares");
+        ASSERT_EQ_UINT64(0, zero.total_accepted, "zero total accepted");
+        ASSERT_EQ_UINT64(0, zero.total_rejected, "zero total rejected");
+    }
+
+    printf("\n--- STRATUM_MAX_JOBS constant ---\n");
+    {
+        ASSERT(STRATUM_MAX_JOBS >= 1, "STRATUM_MAX_JOBS >= 1");
+    }
+
+    printf("\n--- STRATUM_MAX_JOB_ID_LEN constant ---\n");
+    {
+        ASSERT(STRATUM_MAX_JOB_ID_LEN >= 16, "STRATUM_MAX_JOB_ID_LEN >= 16");
+    }
+
+    TEST_SUMMARY();
+}