Add skill-image-gen plugin: AI image generation with OpenAI and Gemini (#1696)

Adds a skill that lets users generate images (icons, sprites, textures,
mockups) directly from their coding workflow using OpenAI gpt-image-2 or
Google Gemini. BYO API key — the skill guides users through setup on
first use.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

plugins/skill-image-gen/.github/plugin/plugin.json

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+{
+  "name": "skill-image-gen",
+  "description": "Generate images using AI directly from your coding workflow. Supports OpenAI (gpt-image-2) and Google Gemini. BYO API key — the skill guides you through setup on first use.",
+  "version": "1.0.0",
+  "keywords": [
+    "image-generation",
+    "openai",
+    "gemini",
+    "ai",
+    "art",
+    "sprites",
+    "textures",
+    "icons"
+  ],
+  "author": {
+    "name": "adamd9",
+    "url": "https://github.com/adamd9"
+  },
+  "homepage": "https://github.com/adamd9/skill-image-gen",
+  "repository": "https://github.com/github/awesome-copilot",
+  "license": "MIT",
+  "skills": [
+    "./skills/generate-image/"
+  ]
+}

plugins/skill-image-gen/README.md

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+# Skill Image Gen
+
+Generate images using AI directly from your coding workflow. Supports **OpenAI (gpt-image-2)** and **Google Gemini (Nano Banana)**.
+
+## What it does
+
+Use natural language to generate images — icons, sprites, textures, mockups, artwork — without leaving your editor. The skill handles API calls, file saving, and guides you through setup on first use.
+
+## Providers
+
+| Provider | Model | Strengths |
+|---|---|---|
+| OpenAI | gpt-image-2 | High quality, excellent text rendering |
+| Google Gemini | gemini-2.0-flash-exp | Fast, free tier available |
+
+## Setup
+
+BYO API key. On first use, the skill walks you through:
+
+1. Choosing a provider
+2. Getting an API key ([OpenAI](https://platform.openai.com/api-keys) · [Gemini](https://aistudio.google.com/apikey))
+3. Setting the environment variable (`SKILL_IMAGE_GEN_OPENAI_KEY` or `SKILL_IMAGE_GEN_GEMINI_KEY`)
+
+## Usage
+
+Ask Copilot to generate an image:
+
+- "Generate a pixel art treasure chest"
+- "Create a seamless grass texture for my game"
+- "Make a minimalist logo for my app"
+
+## Links
+
+- **Source repo**: [adamd9/skill-image-gen](https://github.com/adamd9/skill-image-gen)
+- **License**: MIT