Fix database trait bounds and compilation issues

- Fix KeySource::Generated usage in tests
- Add proper trait bounds for generic database operations
- Remove problematic database operations from generic implementations
- Add concrete implementations for database-specific methods

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: CodingAnarchy

src/encryption.rs

@@ -106,6 +106,10 @@ pub enum EncryptionError {
     /// Cryptographic operation error.
     #[error("Cryptographic error: {0}")]
     Cryptographic(String),
+
+    /// Database operation error.
+    #[error("Database error: {0}")]
+    DatabaseError(String),
 }
 
 /// Supported encryption algorithms.