feat(cli): Add --exclude-relationships and relationship filtering

[tasuku43]

This PR introduces relationship-level filtering and a clearer CLI for excluding edges at render time.

Closes #27

Summary

• Add --exclude-relationships (CSV) to the CLI to hide specific relationship types: dependency, composition, inheritance, realization. Aliases supported (dep/comp/extends/implements).
• Introduce Relationships collection to encapsulate relationship storage, sorting, and filtering.
• Expand RenderOptions with explicit required flags and a RenderOptions::default() factory.
• Wire filtering in ClassDiagram::render() via Relationships::filter(RenderOptions).
• Update README and ARCHITECTURE to document the new option and flags.
• Remove legacy flag --only-properties-deps and previous --exclude (no compatibility kept as requested).

Why

• Make filtering behavior explicit and composable by relationship type.
• Clarify CLI semantics by naming the target domain (relationships).

Details

• Public API: RenderOptions now requires 4 boolean args; use RenderOptions::default() for defaults.
• Renderer: ClassDiagram now holds Relationships instead of an array.
• Behavior: Defaults remain unchanged; your output stays the same unless you pass an exclude list.

Examples

• Hide dependencies and compositions:
  vendor/bin/mermaid-class-diagram generate --path src --exclude-relationships dependency,composition
• Hide only dependencies:
  vendor/bin/mermaid-class-diagram generate --path src --exclude-relationships dependency

Testing

• PHPUnit: all tests pass locally (37 tests, 64 assertions).

Notes

• Future room: add complementary --include-relationships if desired for explicit whitelisting.