Add Ruby AST support using tree-sitter-ruby

- Added `tree-sitter-ruby` dependency to `Cargo.toml` and `Cargo.lock`.
- Introduced `patterns/ruby.rs` with Ruby-specific AST patterns for vulnerability detection.
- Updated `patterns/mod.rs` and `ast.rs` to support Ruby AST parsing and pattern registry initialization.

src/ast.rs

@@ -32,6 +32,7 @@ pub(crate) fn run_rules_on_file(
     Some("py")  => (Language::from(tree_sitter_python::LANGUAGE),                 "python"),
     Some("ts")  => (Language::from(tree_sitter_typescript::LANGUAGE_TYPESCRIPT),  "typescript"),
     Some("js")  => (Language::from(tree_sitter_javascript::LANGUAGE),             "javascript"),
+    Some("rb")  => (Language::from(tree_sitter_ruby::LANGUAGE),                    "ruby"),
     _           => return Ok(vec![]),
   };