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, 46 insertions, 0 deletions

diff --git a/main/relay_selector.h b/main/relay_selector.h
new file mode 100644
index 0000000..4403944
--- /dev/null
+++ b/main/relay_selector.h
@@ -0,0 +1,46 @@
+#ifndef RELAY_SELECTOR_H
+#define RELAY_SELECTOR_H
+
+#include "esp_err.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/semphr.h"
+#include <stdbool.h>
+#include <stdint.h>
+
+#define RELAY_SELECTOR_MAX_RELAYS 8
+#define RELAY_SELECTOR_URL_LEN   128
+
+typedef struct {
+    char url[RELAY_SELECTOR_URL_LEN];
+    char name[64];
+    uint32_t latency_ms;
+    bool supports_nip77;
+    bool alive;
+    int consecutive_failures;
+    uint32_t last_probe_time;
+    uint8_t supported_nips[32];
+    size_t nips_count;
+} relay_info_t;
+
+typedef struct {
+    relay_info_t relays[RELAY_SELECTOR_MAX_RELAYS];
+    size_t count;
+    int primary_idx;
+    int fallback_idx;
+    uint32_t last_full_probe;
+    SemaphoreHandle_t lock;
+} relay_selector_t;
+
+esp_err_t relay_selector_init(relay_selector_t *sel);
+void relay_selector_destroy(relay_selector_t *sel);
+
+esp_err_t relay_selector_probe_all(relay_selector_t *sel);
+
+const relay_info_t *relay_selector_get_primary(relay_selector_t *sel);
+const relay_info_t *relay_selector_get_fallback(relay_selector_t *sel, int idx);
+
+void relay_selector_report_disconnect(relay_selector_t *sel, const char *url);
+
+esp_err_t relay_selector_seed_from_config(relay_selector_t *sel);
+
+#endif