Enhances output options and adds project documentation

[JVBotelho]

Improves the flexibility and security of output file handling, and adds comprehensive project documentation and metadata.

• Output Handling:

  • The --output argument now accepts existing directories, writing to ghosthound_output.json within them.
  • Performs upfront validation of output paths and parent directories, providing clearer error messages.
  • Standardizes output file permissions to 0600 on Unix systems to restrict access to generated JSON.
  • Moves output path resolution and file writing logic to a dedicated output module for improved modularity.
  • Adds a --no-banner flag to suppress the startup banner, which is useful for scripting.

• Project Documentation & Metadata:

  • Adds a CONTRIBUTING.md guide with detailed instructions on toolchain, local checks, dependencies, and vulnerability reporting.
  • Includes a CITATION.cff file for formal citation metadata, enhancing discoverability and proper attribution.
  • Updates README.md to reflect new output behavior, the required Rust version (1.85+), and links to new documentation.
  • Adds authors and homepage metadata to all crate Cargo.toml files.