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, 33 insertions, 0 deletions

diff --git a/components/wisp_relay/broadcaster.c b/components/wisp_relay/broadcaster.c
new file mode 100644
index 0000000..738cbdb
--- /dev/null
+++ b/components/wisp_relay/broadcaster.c
@@ -0,0 +1,33 @@
+#include "broadcaster.h"
+#include "relay_core.h"
+#include "router.h"
+#include "sub_manager.h"
+#include "esp_log.h"
+
+static const char *TAG = "broadcaster";
+
+void broadcaster_fanout_json(relay_ctx_t *ctx, const char *event_json,
+                             size_t event_len, int event_kind,
+                             const char *event_pubkey_hex,
+                             uint64_t event_created_at)
+{
+    if (!ctx || !ctx->sub_manager) return;
+
+    sub_match_result_t matches;
+    sub_manager_match_json(ctx->sub_manager, event_json, event_len, event_kind,
+                           event_pubkey_hex, event_created_at, &matches);
+
+    if (matches.count == 0) {
+        ESP_LOGD(TAG, "No subscribers for event kind=%d", event_kind);
+        return;
+    }
+
+    ESP_LOGD(TAG, "Broadcasting event kind=%d to %d subscriptions",
+             event_kind, matches.count);
+
+    for (uint8_t i = 0; i < matches.count; i++) {
+        sub_match_entry_t *entry = &matches.matches[i];
+        router_send_event(ctx, entry->conn_fd, entry->sub_id,
+                          event_json, event_len);
+    }
+}