fix: resolve all revive linter issues

Added missing package comments:
- cmd/secret/main.go
- internal/cli/cli.go
- internal/secret/constants.go
- internal/vault/management.go
- pkg/bip85/bip85.go

Fixed comment format issues for exported items:
- EnvStateDir, EnvMnemonic, EnvUnlockPassphrase, EnvGPGKeyID in constants.go
- Metadata, UnlockerMetadata, SecretMetadata, Configuration in metadata.go
- AppBIP39, AppHDWIF, AppXPRV in bip85.go

Replaced unused parameters with underscore (_):
- generate.go:39 - parameter 'args'
- init.go:30 - parameter 'args'
- unlockers.go:39,77,102 - parameter 'args' or 'cmd'
- vault.go:37 - parameter 'args'
- management.go:34 - parameter 'target'

internal/secret/constants.go

@@ -1,3 +1,4 @@
+// Package secret provides core types and constants for the secret application.
 package secret
 
 import "os"
@@ -6,11 +7,14 @@ const (
 	// AppID is the unique identifier for this application
 	AppID = "berlin.sneak.pkg.secret"
 
-	// Environment variable names
-	EnvStateDir         = "SB_SECRET_STATE_DIR"
-	EnvMnemonic         = "SB_SECRET_MNEMONIC"
+	// EnvStateDir is the environment variable for specifying the state directory
+	EnvStateDir = "SB_SECRET_STATE_DIR"
+	// EnvMnemonic is the environment variable for providing the mnemonic phrase
+	EnvMnemonic = "SB_SECRET_MNEMONIC"
+	// EnvUnlockPassphrase is the environment variable for providing the unlock passphrase
 	EnvUnlockPassphrase = "SB_UNLOCK_PASSPHRASE" //nolint:gosec // G101: This is an env var name, not a credential
-	EnvGPGKeyID         = "SB_GPG_KEY_ID"
+	// EnvGPGKeyID is the environment variable for providing the GPG key ID
+	EnvGPGKeyID = "SB_GPG_KEY_ID"
 )
 
 // File system permission constants