fix: resolve critical security vulnerabilities in debug logging and command execution

- Remove sensitive data from debug logs (vault/secrets.go, secret/version.go)
- Add input validation for GPG key IDs and keychain item names
- Resolve GPG key IDs to full fingerprints before storing in metadata
- Add comprehensive test coverage for validation functions
- Add golangci-lint configuration with additional linters

Security improvements:
- Debug logs no longer expose decrypted secret values or private keys
- GPG and keychain commands now validate input to prevent injection attacks
- All validation uses precompiled regex patterns for performance

internal/secret/version.go

@@ -343,7 +343,6 @@ func (sv *SecretVersion) GetValue(ltIdentity *age.X25519Identity) ([]byte, error
 	Debug("Successfully retrieved version value",
 		"version", sv.Version,
 		"value_length", len(value),
-		"value_as_string", string(value),
 		"is_empty", len(value) == 0)
 	return value, nil
 }