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, 32 insertions, 2 deletions

diff --git a/sdkconfig b/sdkconfig
index 53590c2..75f2a12 100644
--- a/sdkconfig
+++ b/sdkconfig
@@ -897,7 +897,7 @@ CONFIG_HTTPD_MAX_URI_LEN=512
 CONFIG_HTTPD_ERR_RESP_NO_DELAY=y
 CONFIG_HTTPD_PURGE_BUF_LEN=32
 # CONFIG_HTTPD_LOG_PURGE_DATA is not set
-# CONFIG_HTTPD_WS_SUPPORT is not set
+CONFIG_HTTPD_WS_SUPPORT=y
 # CONFIG_HTTPD_QUEUE_WORK_BLOCKING is not set
 CONFIG_HTTPD_SERVER_EVENT_POST_TIMEOUT=2000
 # end of HTTP Server
@@ -1526,7 +1526,7 @@ CONFIG_LWIP_DNS_SUPPORT_MDNS_QUERIES=y
 # CONFIG_LWIP_IRAM_OPTIMIZATION is not set
 # CONFIG_LWIP_EXTRA_IRAM_OPTIMIZATION is not set
 CONFIG_LWIP_TIMERS_ONDEMAND=y
-CONFIG_LWIP_MAX_SOCKETS=10
+CONFIG_LWIP_MAX_SOCKETS=20
 # CONFIG_LWIP_USE_ONLY_LWIP_SELECT is not set
 # CONFIG_LWIP_SO_LINGER is not set
 CONFIG_LWIP_SO_REUSE=y
@@ -2101,6 +2101,36 @@ CONFIG_WIFI_PROV_AUTOSTOP_TIMEOUT=30
 CONFIG_WIFI_PROV_STA_ALL_CHANNEL_SCAN=y
 # CONFIG_WIFI_PROV_STA_FAST_SCAN is not set
 # end of Wi-Fi Provisioning Manager
+
+#
+# LittleFS
+#
+# CONFIG_LITTLEFS_SDMMC_SUPPORT is not set
+CONFIG_LITTLEFS_MAX_PARTITIONS=3
+CONFIG_LITTLEFS_PAGE_SIZE=256
+CONFIG_LITTLEFS_OBJ_NAME_LEN=64
+CONFIG_LITTLEFS_READ_SIZE=128
+CONFIG_LITTLEFS_WRITE_SIZE=128
+CONFIG_LITTLEFS_LOOKAHEAD_SIZE=128
+CONFIG_LITTLEFS_CACHE_SIZE=512
+CONFIG_LITTLEFS_BLOCK_CYCLES=512
+CONFIG_LITTLEFS_USE_MTIME=y
+# CONFIG_LITTLEFS_USE_ONLY_HASH is not set
+# CONFIG_LITTLEFS_HUMAN_READABLE is not set
+CONFIG_LITTLEFS_MTIME_USE_SECONDS=y
+# CONFIG_LITTLEFS_MTIME_USE_NONCE is not set
+# CONFIG_LITTLEFS_SPIFFS_COMPAT is not set
+# CONFIG_LITTLEFS_FLUSH_FILE_EVERY_WRITE is not set
+# CONFIG_LITTLEFS_FCNTL_GET_PATH is not set
+# CONFIG_LITTLEFS_MULTIVERSION is not set
+# CONFIG_LITTLEFS_MALLOC_STRATEGY_DISABLE is not set
+CONFIG_LITTLEFS_MALLOC_STRATEGY_DEFAULT=y
+# CONFIG_LITTLEFS_MALLOC_STRATEGY_INTERNAL is not set
+# CONFIG_LITTLEFS_MALLOC_STRATEGY_SPIRAM is not set
+CONFIG_LITTLEFS_ASSERTS=y
+# CONFIG_LITTLEFS_MMAP_PARTITION is not set
+# CONFIG_LITTLEFS_WDT_RESET is not set
+# end of LittleFS
 # end of Component config
 
 # CONFIG_IDF_EXPERIMENTAL_FEATURES is not set