feat: local Nostr relay with relay selection, sync, and integration tests

Local Nostr relay (NIP-01) on port 4869 with LittleFS 4MB storage.
All events published locally first, then synced to public relays via REQ-diff.
Relay selection via NIP-11 HTTP probing with NIP-77 scoring and auto-failover.

Components:
- wisp_relay: 16-file local relay (ws_server, storage_engine, sub_manager,
  broadcaster, relay_validator, router, handlers, rate_limiter, nip11,
  deletion, flash_monitor, relay_types)
- esp_littlefs: LittleFS VFS integration (git submodule)
- negentropy: for future NIP-77 binary sync (git submodule)

New source files:
- local_relay.c/h: thin wrapper for relay init/start/publish
- relay_selector.c/h: NIP-11 probe + scoring + auto-failover
- sync_manager.c/h: REQ-diff sync (primary 30min, fallback 6h)

Bug fixes:
- config.c: use-after-free (cJSON_Delete before seed_relays/sync parsing)
- local_relay: moved init to app_main for boot-time start (not gated on STA IP)

Flash layout: 4MB LittleFS partition at 0x500000 for relay_store

Test results (Board B, live hardware):
- Smoke: ping + HTTP 4869 + NIP-11: PASS
- NIP-11 info document: 10/11 PASS
- WS pub/sub (connect, REQ/EOSE, EVENT/OK, CLOSE, concurrent): 6/6 PASS
- Unit tests (relay_validator + relay_selector): 13/13 PASS

Hardware test make targets in physical-router-test-automation/:
- make relay-build, relay-flash-b, relay-test-smoke/nip11/pubsub/sync/full

1 files changed, 53 insertions, 0 deletions

diff --git a/components/wisp_relay/nip11_relay.c b/components/wisp_relay/nip11_relay.c
new file mode 100644
index 0000000..4e1df37
--- /dev/null
+++ b/components/wisp_relay/nip11_relay.c
@@ -0,0 +1,53 @@
+#include "nip11_relay.h"
+#include <string.h>
+
+static const char *NIP11_JSON =
+"{"
+  "\"name\":\"TollGate Relay\","
+  "\"description\":\"Local Nostr relay with 21-day TTL and negentropy sync\","
+  "\"pubkey\":\"\","
+  "\"contact\":\"\","
+  "\"supported_nips\":[1,9,11,20,40,77],"
+  "\"software\":\"https://github.com/nicobao/esp32-tollgate\","
+  "\"version\":\"1.0.0\","
+  "\"limitation\":{"
+    "\"max_message_length\":65536,"
+    "\"max_subscriptions\":8,"
+    "\"max_filters\":4,"
+    "\"max_limit\":500,"
+    "\"max_subid_length\":64,"
+    "\"max_event_tags\":100,"
+    "\"max_content_length\":32768,"
+    "\"min_pow_difficulty\":0,"
+    "\"auth_required\":false,"
+    "\"payment_required\":false"
+  "},"
+  "\"retention\":[{\"kinds\":[0,1,2,3,4,5,6,7],\"time\":1814400}],"
+  "\"relay_countries\":[\"DE\"]"
+"}";
+
+esp_err_t relay_nip11_handler(httpd_req_t *req)
+{
+    char accept[64] = "";
+    httpd_req_get_hdr_value_str(req, "Accept", accept, sizeof(accept));
+
+    if (strstr(accept, "application/nostr+json")) {
+        httpd_resp_set_type(req, "application/nostr+json");
+    } else {
+        httpd_resp_set_type(req, "application/json");
+    }
+
+    httpd_resp_set_hdr(req, "Access-Control-Allow-Origin", "*");
+    httpd_resp_set_hdr(req, "Access-Control-Allow-Headers", "Content-Type, Accept");
+    httpd_resp_set_hdr(req, "Access-Control-Allow-Methods", "GET, OPTIONS");
+    return httpd_resp_send(req, NIP11_JSON, strlen(NIP11_JSON));
+}
+
+esp_err_t relay_nip11_options_handler(httpd_req_t *req)
+{
+    httpd_resp_set_hdr(req, "Access-Control-Allow-Origin", "*");
+    httpd_resp_set_hdr(req, "Access-Control-Allow-Headers", "Content-Type, Accept");
+    httpd_resp_set_hdr(req, "Access-Control-Allow-Methods", "GET, OPTIONS");
+    httpd_resp_set_status(req, "204 No Content");
+    return httpd_resp_send(req, NULL, 0);
+}