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, 45 insertions, 0 deletions

diff --git a/components/wisp_relay/relay_validator.h b/components/wisp_relay/relay_validator.h
new file mode 100644
index 0000000..c07308f
--- /dev/null
+++ b/components/wisp_relay/relay_validator.h
@@ -0,0 +1,45 @@
+#ifndef RELAY_VALIDATOR_H
+#define RELAY_VALIDATOR_H
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stddef.h>
+
+typedef enum {
+    VALIDATION_OK = 0,
+    VALIDATION_ERR_SCHEMA,
+    VALIDATION_ERR_ID,
+    VALIDATION_ERR_SIG,
+    VALIDATION_ERR_EXPIRED,
+    VALIDATION_ERR_FUTURE,
+    VALIDATION_ERR_DUPLICATE,
+    VALIDATION_ERR_POW,
+    VALIDATION_ERR_BLOCKED,
+    VALIDATION_ERR_TOO_OLD,
+} validation_result_t;
+
+typedef struct {
+    uint32_t max_event_age_sec;
+    int64_t max_future_sec;
+    uint8_t min_pow_difficulty;
+    bool check_duplicates;
+} validator_config_t;
+
+typedef struct relay_event relay_event_t;
+typedef struct storage_engine storage_engine_t;
+
+validation_result_t relay_validator_check(const uint8_t *id,
+                                           const uint8_t *pubkey,
+                                           uint64_t created_at,
+                                           int kind,
+                                           const char *content,
+                                           size_t content_len,
+                                           const char *tags_json,
+                                           const uint8_t *sig,
+                                           const validator_config_t *config);
+
+bool relay_validator_verify_event(const char *event_json, size_t event_len);
+
+const char *relay_validator_result_string(validation_result_t result);
+
+#endif