Phase 7: MCP handler (25 tests), NIP-04 encrypt/decrypt (15 tests), CVM server skeleton

- mcp_handler.c/h: 4 tools (get_config, set_config, get_balance, wallet_send)
- nip04.c/h: AES-256-CBC + ECDH with 0x02 compressed pubkey prefix
  - Fixed IV copy bug: mbedTLS AES-CBC modifies IV in-place
  - Base64 encode/decode for ciphertext transport
  - PKCS7 padding
- cvm_server.c/h: Nostr DM listener with FreeRTOS task
- config: cvm_enabled, cvm_relays fields
- 156 total tests passing across 10 test binaries

1 files changed, 13 insertions, 0 deletions

diff --git a/main/nip04.h b/main/nip04.h
new file mode 100644
index 0000000..f612a8e
--- /dev/null
+++ b/main/nip04.h
@@ -0,0 +1,13 @@
+#ifndef NIP04_H
+#define NIP04_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+void nip04_encrypt(const uint8_t *sender_privkey, const uint8_t *recipient_pubkey,
+                   const char *plaintext, uint8_t *ciphertext_base64, size_t *out_len);
+
+int nip04_decrypt(const uint8_t *recipient_privkey, const uint8_t *sender_pubkey,
+                  const char *ciphertext_base64, char *plaintext, size_t plaintext_max);
+
+#endif