feat: add CLI-dependent skills

[ziyiunity]

Adds CLI-dependent skills.

Where the first set is mostly guidance, these skills read and change the project itself: they inspect the scene and assets, apply settings, and verify the result rather than describing what to do. Nine of them do that by running C# in a live Unity Editor, so they ship together with unity-cli, which is the skill that owns getting a working CLI and a reachable Editor.

Getting started and tooling

Skill	What it does
/new-unity-project	Guided flow for a brand-new project. Gathers the concept and target platforms, installs the Editor while it asks, then creates the project, source control, and packages.
/unity-cli	Drive Unity from the terminal, including a running Editor: create and modify GameObjects, edit scenes and assets, inspect the hierarchy, run C#. Also editor installs, licences, builds, and logs.
/unity-package-management	Add, remove, upgrade, and discover UPM packages from outside the Editor, including headless and CI installs.

Audio

Skill	What it does
/audio-setup-mixers	Classifies every Audio Source by what it plays and routes it into the right Audio Mixer Group. Reports anything it could not match instead of silently skipping it.
/optimize-audio	Cuts audio memory and CPU cost through import settings and mixer configuration. Picks the right Load Type for short clips against music against ambient beds.
/setup-vivox-voice-chat	In-game voice and text chat with Unity Vivox. Microphone permissions on Android and iOS, voice activity detection tuning, and mute and volume controls in a settings UI.

Graphics and Web

Skill	What it does
/urp-postprocessing	Set up and debug URP post-processing through the Volume framework: bloom, tonemapping, colour adjustments, depth of field, vignette, motion blur.
/optimize-web	Smaller downloads and faster loads for WebGL and WebGPU builds. Compression, stripping, exception handling, memory, and browser-side profiling.

Scene and gameplay

Skill	What it does
/initialize-ai-navigation	Set up AI Navigation: NavMesh surfaces and agents, obstacles, links, modifiers, areas and costs. Walkable meshes, pathfinding, patrol routes.
/physics-3d-collision	Diagnose 3D PhysX collision and trigger problems. Collision or trigger callbacks not firing, objects passing through each other, raycasts missing, forces that stop working.
/sprite-editor	Edit sprite rectangles, borders, pivots, and outlines, and slice sprite sheets automatically, on a grid, or isometrically.