feat(self-hosting): direct LLVM C-API & LLD in-process linking, full …

[rohitsoni007]

Direct In-Process LLVM & LLD Linker

• In-Memory Compilation & Linking: Replaced external clang and lld-link subprocesses with direct LLVM C-API code emission and in-process lld::coff::link.
• Zero-Dependency Monolithic Executable: Statically linked LLVM*.lib and lld*.lib into a single standalone zuv.exe (~106 MB) with zero external DLLs.

🔌 C Foreign Function Interface (extern / ffi)

• Native C ABI Declarations: Added extern "<lib>" <func> <params> -> <retType> syntax in pure Zuv and C++ bootstrap compiler.
• Direct LLVM C-API in Pure Zuv: Declared and orchestrated target initialization, IR parsing, target machine creation, and object emission directly in cli.zv.
• Dynamic Library Linking: Automatically links Windows system libraries (user32, kernel32, ntdll, ws2_32) and custom .lib files.