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, 3 insertions, 0 deletions

diff --git a/main/config.h b/main/config.h
index 86b5e1a..fa4d95c 100644
--- a/main/config.h
+++ b/main/config.h
@@ -60,6 +60,9 @@ typedef struct {
     int client_retry_interval_ms;
 
     payout_config_t payout;
+
+    bool cvm_enabled;
+    char cvm_relays[256];
 } tollgate_config_t;
 
 void tollgate_config_derive_unique(tollgate_config_t *cfg);