Phase 3: Nostr identity derivation + wifistr service discovery

- Add identity.c/h: HMAC-SHA512 derivation from nsec → npub, STA/AP MAC, SSID, AP IP
- Add nostr_event.c/h: NIP-01 event serialization + Schnorr signing (BIP-340)
- Add geohash.c/h: lat/lon to geohash encoding
- Add wifistr.c/h: kind 38787 event builder + WebSocket publish to Nostr relays
- Update config.c/h: nsec-based identity, Nostr relay/geo config, remove static SSID/IP
- Replace custom mbedTLS wallet with nucula library (libsecp256k1)
- Remove wallet.c/h, wallet_persist.c/h (replaced by nucula_lib component)
- Verified on Board A: derived SSID, captive portal, payment, wallet, wifistr publish

1 files changed, 10 insertions, 0 deletions

diff --git a/main/wifistr.h b/main/wifistr.h
new file mode 100644
index 0000000..843b6be
--- /dev/null
+++ b/main/wifistr.h
@@ -0,0 +1,10 @@
+#ifndef WIFISTR_H
+#define WIFISTR_H
+
+#include "esp_err.h"
+
+esp_err_t wifistr_publish(void);
+
+void wifistr_start_periodic(int interval_s);
+
+#endif