feat(swift): add extension detection, inheritance edges, and type kind

[lngyeen]

Summary

• Extension detection: Fixed _get_name() to extract names from user_type > type_identifier for Swift extensions — previously extensions were silently dropped because the name was nested one level deeper than the generic path expected.
• Inheritance/conformance edges: Added Swift branch to _get_bases() that walks inheritance_specifier > user_type > type_identifier — previously zero INHERITS edges were produced for any Swift file.
• Type differentiation: Populated extra["swift_kind"] with the actual keyword (class/struct/enum/actor/extension/protocol) following the same pattern as Solidity's extra["solidity_kind"].

Motivation

Swift's Tree-sitter grammar maps struct, enum, actor, and extension declarations all to class_declaration nodes. The existing parser handled the first three correctly (since type_identifier is a direct child), but extensions use user_type > type_identifier for the extended type name, which was not traversed.

Similarly, Swift uses inheritance_specifier > user_type > type_identifier for protocol conformances and class inheritance, but _get_bases() had no Swift-specific branch, resulting in zero inheritance edges.

These gaps are significant for Swift projects using Clean Architecture (protocol-oriented design, extensions for conformance, actors for isolation).

Changes

File	Change
parser.py:_get_name()	Added Swift extension name extraction via user_type
parser.py:_get_bases()	Added Swift inheritance_specifier traversal
parser.py:_extract_classes()	Populate extra["swift_kind"] from keyword child
tests/fixtures/sample.swift	Added enum, actor, and extension samples
tests/test_multilang.py	Added 6 new tests for enum, actor, extension, protocol, swift_kind, and inheritance edges

Test plan

• All 9 Swift tests pass (TestSwiftParsing)
• All 621 tests pass with zero regressions
• Verified AST structure with Tree-sitter Swift grammar directly