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, 88 insertions, 0 deletions

diff --git a/components/wisp_relay/storage_engine.h b/components/wisp_relay/storage_engine.h
new file mode 100644
index 0000000..4e17113
--- /dev/null
+++ b/components/wisp_relay/storage_engine.h
@@ -0,0 +1,88 @@
+#ifndef STORAGE_ENGINE_H
+#define STORAGE_ENGINE_H
+
+#include <stdbool.h>
+#include <stdint.h>
+#include "esp_err.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/semphr.h"
+#include "freertos/task.h"
+
+#define STORAGE_MAX_EVENTS         5000
+#define STORAGE_MAX_EVENT_SIZE     8192
+#define STORAGE_INDEX_ENTRIES      5000
+#define STORAGE_PARTITION_LABEL    "relay_store"
+
+typedef enum {
+    STORAGE_OK = 0,
+    STORAGE_ERR_NOT_INITIALIZED,
+    STORAGE_ERR_FULL,
+    STORAGE_ERR_DUPLICATE,
+    STORAGE_ERR_NOT_FOUND,
+    STORAGE_ERR_IO,
+    STORAGE_ERR_NO_MEM,
+    STORAGE_ERR_SERIALIZE
+} storage_error_t;
+
+#define STORAGE_FLAG_DELETED  0x01
+
+typedef struct __attribute__((packed)) {
+    uint8_t  event_id[32];
+    uint32_t created_at;
+    uint32_t expires_at;
+    uint32_t file_index;
+    uint16_t kind;
+    uint8_t  pubkey_prefix[4];
+    uint8_t  flags;
+    uint8_t  reserved;
+} storage_index_entry_t;
+
+typedef struct {
+    uint32_t total_events;
+    uint32_t total_bytes;
+    uint32_t free_bytes;
+    uint32_t oldest_event_ts;
+    uint32_t newest_event_ts;
+} storage_stats_t;
+
+typedef struct storage_engine {
+    storage_index_entry_t *index;
+    uint16_t index_count;
+    uint16_t max_index_entries;
+    uint32_t next_file_index;
+    SemaphoreHandle_t lock;
+    TaskHandle_t cleanup_task;
+    bool initialized;
+    bool cleanup_stop;
+    char mount_point[16];
+    uint32_t default_ttl_sec;
+} storage_engine_t;
+
+esp_err_t storage_init(storage_engine_t *engine, uint32_t default_ttl_sec);
+void storage_destroy(storage_engine_t *engine);
+
+storage_error_t storage_save_event_json(storage_engine_t *engine,
+                                        const char *event_json,
+                                        size_t event_json_len);
+
+storage_error_t storage_query_events_json(storage_engine_t *engine,
+                                          int kind,
+                                          const char *author_hex,
+                                          int limit,
+                                          char ***results,
+                                          uint16_t *count);
+
+void storage_free_query_results(char **results, uint16_t count);
+
+bool storage_event_exists(storage_engine_t *engine, const uint8_t event_id[32]);
+
+storage_error_t storage_delete_event(storage_engine_t *engine, const uint8_t event_id[32]);
+
+int storage_purge_expired(storage_engine_t *engine);
+int storage_compact_index(storage_engine_t *engine);
+
+void storage_get_stats(storage_engine_t *engine, storage_stats_t *stats);
+
+esp_err_t storage_start_cleanup_task(storage_engine_t *engine);
+
+#endif