* feat: add Swift language support
Add tree-sitter-swift extractor for classes, structs, protocols,
functions, imports, and call graph edges. Includes 8 passing tests.
* feat: full Swift AST support — enums, extensions, actors, conformance
- Enums: extract enum types, methods, and cases (case_of edges)
- Extensions: methods attach to the original type (no duplicate nodes)
- Actors: recognized via unified class_declaration node type
- Conformance/inheritance: inherits edges from : Protocol syntax
- deinit/subscript: name resolution for nameless declarations
- 12 new tests (110 total, all passing)
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