Add Copilot instructions for development workflow (#35)

- Add concise guidelines for test cases and commits
- Enforce English for commit messages and PR descriptions
- Specify documentation language requirements
- Keep instructions minimal and actionable

Author: wysaid

.github/copilot-instructions.md

@@ -0,0 +1,8 @@
+# GitHub Copilot Instructions for CameraCapture
+
+## Code Guidelines
+- Add/adjust test cases when fixing bugs or adding features
+- Run all tests before commit
+- Use English for git commit messages and PR descriptions
+- All `.md` files in `docs/` must be in English
+- Only commit necessary new `.md` files after review.