fix: split infrastructure if-chains to prevent if-drop bug

[cs01]

Summary

• Splits 3 infrastructure functions that exceeded the 4-branch if-return safety limit
• getBuiltinAstTypeByName() in type-resolver.ts: 15 → 3 sub-functions (4 each) + 4-branch coordinator
• llvmTypeToSymbolKind() in function-generator.ts: 9 → 2 sub-methods (4 each) + 3-branch coordinator
• resolve() in type-context.ts: 9 → 2 sub-methods (4 each) + 4-branch coordinator
• Prevents the native compiler's if-drop bug (5th+ consecutive if-return blocks silently dropped)

Test plan

• All 434 tests pass
• Self-hosting verification passes (verify:quick)

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