Add CLAUDE.md: AI assistant guide for MMO project

[bryfur]

Summary

Added comprehensive CLAUDE.md documentation to guide AI assistants (like Claude) working on the MMO project. This file serves as a quick reference for project structure, architecture, build instructions, and coding conventions.

Key Changes

• Project Overview: High-level description of the 3D MMO architecture (C++20, SDL3, EnTT ECS, Jolt Physics, Asio networking)
• Quick Reference: Essential build and run commands with critical warnings about avoiding clean rebuilds
• Critical Rules: Documented build best practices, testing approach, and shader compilation requirements
• Repository Structure: Complete directory layout with descriptions of each major component
• Architecture Documentation:
  • ECS pattern and component/system organization
  • Networking layer (TCP, serialization, connection flow)
  • Rendering pipeline (SDL3 GPU, HLSL shaders, features)
  • Physics integration (Jolt, collision layers, server-authoritative)
• Coding Conventions: Naming standards (enforced by clang-tidy), namespace organization, formatting rules, coordinate system, and shader conventions
• Build System: CMake configuration, dependency management, and CI setup
• Key Files Reference: Table of important files with their purposes

Notable Details

• Emphasizes that incremental builds are mandatory (clean rebuilds take excessive time)
• Documents the Y-up coordinate system and radian-based rotations
• Specifies shader binding sets and uniform struct alignment requirements
• Includes complete namespace hierarchy for the project
• References all major dependencies and their integration method (FetchContent)

https://claude.ai/code/session_01XoDW63YfhCcAW74Gwe1sve

[Copilot]

Pull request overview

This PR adds CLAUDE.md, a focused guide for AI assistants working on the MMO project, documenting architecture, build system, conventions, and key project structure so tools can navigate and reason about the codebase effectively.

Changes:

• Introduces a comprehensive project overview covering ECS, networking (Asio/TCP), rendering (SDL3 GPU + HLSL→SPIR-V), and physics (Jolt).
• Documents build and run workflows, repository layout, coding conventions, shader conventions, and dependency management via CMake + FetchContent.
• Adds a quick-reference section listing key files and their roles across client, server, engine, and data layers.

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[Copilot]

The statement that all dependencies are "statically linked and auto-fetched" is slightly misleading for the SDL3/SDL3_ttf/SDL3_image stack: src/engine/CMakeLists.txt first tries find_package and only falls back to vendored static builds when system libraries are missing, so on systems with SDL3 installed they won't actually be auto-fetched or necessarily statically linked. It would be more accurate to clarify that these libraries are vendored and linked statically only when system versions are unavailable or incorrect.

Suggested change

	- Dependencies are statically linked and auto-fetched: SDL3, EnTT, Jolt, Asio, tinygltf, GLM, nlohmann/json, SDL3_ttf, SDL3_image, SDL_shadercross
	- Most dependencies are statically linked and auto-fetched via FetchContent: EnTT, Jolt, Asio, tinygltf, GLM, nlohmann/json, SDL_shadercross
	- SDL3, SDL3_ttf, and SDL3_image are used from system packages when available (via `find_package`) and only auto-fetched / linked statically when suitable system versions are unavailable or incorrect