[US-054-T2] Add bundle validate CLI command with TDD

[KochTobi-Agent]

Task Description

Implement the oc bundle validate [PATH] CLI command using TDD (red-to-green approach).

TDD Cycle

RED Phase - Write Failing Tests

Create comprehensive tests in cmd/bundle_test.go:

• TestBundleValidateCommand_ValidBundle - validates valid bundle, exits 0
• TestBundleValidateCommand_InvalidBundle - validates invalid bundle, exits 1
• TestBundleValidateCommand_DefaultPath - uses current directory when no PATH arg
• TestBundleValidateCommand_ArchivePath - validates .tar.gz archive path
• TestBundleValidateCommand_NonExistentPath - handles non-existent path gracefully
• TestBundleValidateCommand_FormattedOutput - errors formatted with styles package

GREEN Phase - Implement to Pass

Add to cmd/bundle.go:

• bundleValidateCmd cobra.Command with:
  • Use: "validate [PATH]"
  • Short: "Validate bundle structure and manifest"
  • Args: cobra.MaximumNArgs(1)
  • RunE: runBundleValidate
• runBundleValidate(cmd *cobra.Command, args []string) error function:
  • Resolve path (default to "." if no arg)
  • Use bundle.ResolveToLocal() for directory/archive normalization
  • Call bundle.ValidateBundle() from T1
  • Print errors with styles.Error(), warnings with styles.Warning()
  • Exit code 0 on valid, 1 on validation errors, 2 on system errors

Acceptance Criteria

• All CLI tests written and initially failing
• Command implementation passes all tests
• Exit codes: 0 = success, 1 = validation errors, 2 = system/IO errors
• Works with both directories and .tar.gz archives
• Default path (current directory) works when no argument provided
• Follows existing command patterns in cmd/bundle.go