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, 30 insertions, 0 deletions

diff --git a/components/wisp_relay/flash_monitor.c b/components/wisp_relay/flash_monitor.c
new file mode 100644
index 0000000..ceb8c3b
--- /dev/null
+++ b/components/wisp_relay/flash_monitor.c
@@ -0,0 +1,30 @@
+#include "flash_monitor.h"
+#include "esp_littlefs.h"
+#include "esp_log.h"
+#include <string.h>
+
+static const char *TAG = "flash_monitor";
+
+void flash_get_health(const char *partition_label, flash_health_t *health)
+{
+    memset(health, 0, sizeof(flash_health_t));
+
+    esp_err_t ret = esp_littlefs_info(partition_label,
+                                       &health->total_bytes,
+                                       &health->used_bytes);
+    if (ret != ESP_OK) {
+        ESP_LOGE(TAG, "Failed to get LittleFS info: %s", esp_err_to_name(ret));
+        return;
+    }
+
+    if (health->total_bytes == 0) {
+        health->free_bytes = 0;
+        health->usage_percent = 0.0f;
+    } else {
+        health->free_bytes = health->total_bytes - health->used_bytes;
+        health->usage_percent = (float)health->used_bytes / health->total_bytes * 100.0f;
+    }
+
+    ESP_LOGD(TAG, "Flash: %.1f%% used (%zu/%zu bytes)",
+             health->usage_percent, health->used_bytes, health->total_bytes);
+}