fix: use getAllInterfaceFields for function interface parameter metadata

[cs01]

Summary

• FunctionGenerator built ObjectMetadata for interface-typed function parameters using iface.fields directly — only own fields, missing inherited ones from extends
• Added getAllInterfaceFields(iface: InterfaceDeclaration): InterfaceField[] to FunctionGeneratorContext interface (already implemented by LLVMGenerator.getAllInterfaceFields)
• Changed inline anonymous type cast to InterfaceDeclaration and call ctx.getAllInterfaceFields(iface) for the field list
• Added test fixture interfaces/interface-extends-param.ts verifying inherited field access inside functions

Test plan

• All 430 unit tests pass (includes new interface-extends-param test)
• Full 3-stage self-hosting passes

🤖 Generated with Claude Code