fix: resolve mnd and nestif linter errors

- Define base85 constants (base85ChunkSize, base85DigitCount, base85Base)
- Replace magic numbers in base85 encoding logic with named constants
- Add nolint:nestif comments for legitimate nested conditionals:
  - crypto.go: Clear separation between secret generation vs retrieval
  - secrets.go: Separate JSON and table output formatting logic
  - vault.go: Separate JSON and text output formatting logic

internal/cli/crypto.go

@@ -74,7 +74,7 @@ func (cli *Instance) Encrypt(secretName, inputFile, outputFile string) error {
 		return fmt.Errorf("failed to check if secret exists: %w", err)
 	}
 
-	if !exists {
+	if !exists { //nolint:nestif // Clear conditional logic for secret generation vs retrieval
 		// Secret doesn't exist, generate new age key and store it
 		identity, err := age.GenerateX25519Identity()
 		if err != nil {