[2.8.3] Fix gemini-imagegen file format documentation

- Add critical documentation about Gemini returning JPEG by default
- Explain that using .jpg extension avoids "Image does not match media type" errors
- Provide PNG conversion example when needed
- Include format verification command

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

plugins/compounding-engineering/.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "compounding-engineering",
-  "version": "2.8.2",
+  "version": "2.8.3",
   "description": "AI-powered development tools. 24 agents, 16 commands, 11 skills, 2 MCP servers for code review, research, design, and workflow automation.",
   "author": {
     "name": "Kieran Klaassen",