Add CLI validator for TOML syntax validation

[dereuromark]

Summary

• Adds toml-validate CLI command for validating TOML file syntax
• Supports stdin input for piping (cat file.toml | toml-validate)
• Optional JSON Schema validation via --schema flag (requires justinrainbow/json-schema)
• Proper exit codes for CI/CD integration

Usage

# Validate a file
toml-validate config.toml

# Pipe from stdin
cat config.toml | toml-validate

# With JSON Schema validation
toml-validate config.toml --schema=schema.json

# Quiet mode for scripting
toml-validate config.toml -q && echo "Valid!"

Exit codes

Code	Meaning
0	Valid TOML
1	Invalid TOML (syntax errors)
2	Schema validation failed
3	File not found / read error

This enables the library to be listed on the TOML validators wiki.