v0.3.4 - Implement secure relay private key storage

- Add relay_seckey table for secure private key storage
- Implement store_relay_private_key() and get_relay_private_key() functions
- Remove relay private key from public configuration events (kind 33334)
- Update first-time startup sequence to store keys securely after DB init
- Add proper validation and error handling for private key operations
- Fix timing issue where private key storage was attempted before DB initialization
- Security improvement: relay private keys no longer exposed in public events

src/sql_schema.h

@@ -1,12 +1,12 @@
 /* Embedded SQL Schema for C Nostr Relay
  * Generated from db/schema.sql - Do not edit manually
- * Schema Version: 4
+ * Schema Version: 5
  */
 #ifndef SQL_SCHEMA_H
 #define SQL_SCHEMA_H
 
 /* Schema version constant */
-#define EMBEDDED_SCHEMA_VERSION "4"
+#define EMBEDDED_SCHEMA_VERSION "5"
 
 /* Embedded SQL schema as C string literal */
 static const char* const EMBEDDED_SCHEMA_SQL = 
@@ -15,7 +15,7 @@ static const char* const EMBEDDED_SCHEMA_SQL =
 -- Event-based configuration system using kind 33334 Nostr events\n\
 \n\
 -- Schema version tracking\n\
-PRAGMA user_version = 4;\n\
+PRAGMA user_version = 5;\n\
 \n\
 -- Enable foreign key support\n\
 PRAGMA foreign_keys = ON;\n\
@@ -58,8 +58,8 @@ CREATE TABLE schema_info (\n\
 \n\
 -- Insert schema metadata\n\
 INSERT INTO schema_info (key, value) VALUES\n\
-    ('version', '4'),\n\
-    ('description', 'Event-based Nostr relay schema with kind 33334 configuration events'),\n\
+    ('version', '5'),\n\
+    ('description', 'Event-based Nostr relay schema with secure relay private key storage'),\n\
     ('created_at', strftime('%s', 'now'));\n\
 \n\
 -- Helper views for common queries\n\
@@ -128,6 +128,13 @@ BEGIN\n\
     AND id != NEW.id;\n\
 END;\n\
 \n\
+-- Relay Private Key Secure Storage\n\
+-- Stores the relay's private key separately from public configuration\n\
+CREATE TABLE relay_seckey (\n\
+    private_key_hex TEXT NOT NULL CHECK (length(private_key_hex) = 64),\n\
+    created_at INTEGER NOT NULL DEFAULT (strftime('%s', 'now'))\n\
+);\n\
+\n\
 -- Persistent Subscriptions Logging Tables (Phase 2)\n\
 -- Optional database logging for subscription analytics and debugging\n\
 \n\