snake_case refactor: entire codebase

[arc-butler]

snake_case Refactor

Converted the entire codebase from Hungarian/PascalCase to snake_case.

What changed

• Types: CApplication → application, SMath → math, FVec2 → vec2, TUInt32 → u32, etc.
• Methods: GetWidth() → get_width(), OnUpdate() → on_update(), SerializeToText() → serialize_to_text()
• Members: mWindow → window_, mData → data_ (trailing underscore convention)
• Parameters: pFilepath → filepath, _DeltaTime → delta_time (stripped p/underscore prefixes)
• Locals: viewportSize → viewport_size, MousePos → mouse_pos
• Enums/values: EKey::LeftControl → key::left_control, Play → play
• Namespace: ARC → arc
• Type aliases: TString → string, TRef → ref, FVec2 → vec2

Conventions

• snake_case for all identifiers
• Trailing _ for member variables
• UPPER_CASE for macros only
• No Hungarian prefixes (C, S, T, F, I, U, E, m, p)
• ARC API surface is now arc::type_name instead of ARC::CTypeName

How it was done

1. clang-tidy readability-identifier-naming for bulk rename (functions, locals, enums, template params)
2. Python post-processing for Hungarian prefix stripping, member variable convention, and edge cases

Status

• 132 files changed, 3862 insertions/3810 deletions
• Will not compile on first try — some edge cases need manual fixing (e.g., template specializations, macro-generated names, include paths)
• Expect ~50-100 compilation errors that need fixing