Documentation update

[eliotttesnier]

This pull request introduces significant improvements to documentation for scripting, contributing, and modding, as well as gameplay and engine changes for obstacle generation, UI navigation, and power-up balancing. The documentation additions provide clear guides for contributors and modders, including a new scripting API reference and tutorials. Gameplay changes include enhanced map obstacle generation, improved UI navigation in pause menus, and more balanced speed power-ups. Minor changes and cleanups are also present.

Documentation Improvements

• Added a comprehensive contribution guide (CONTRIBUTING.md) detailing repository structure, branching, commit conventions, testing, code style, and PR review process.
• Introduced a new scripting documentation section: includes an introduction to Lua scripting (intro.md), a full API reference (api-reference.md), and a step-by-step tutorial for creating custom enemies (tutorial-modding.md). [1] [2] [3]
• Added a category definition for scripting and configuration docs for better navigation in Docusaurus (_category_.json).
• Removed outdated or redundant guide for creating maps, mobs, and projectiles via JSON configs (creating-maps-mobs-projectiles.md).

Gameplay and Engine Enhancements

• Improved obstacle generation in maps by adding a third layer of noise, resulting in more varied and challenging terrain in MapGeneratorSystem.cpp.
• Balanced the speed power-up script to prevent excessive stacking; now only increases speed if below a threshold and by a smaller increment (powerUpSpeed.lua).

UI/UX Improvements

• Enhanced pause menu navigation: enabled navigation, focused the first element on entry, and added navigation input handling in PauseState.cpp. [1] [2]

Minor Changes

• Updated the client startup instructions in README.md to simplify multiplayer setup.