chore: update project documentation and configuration files

- Added AGENTS.md for AI agent documentation and maintainers, outlining project structure and conventions.
- Updated CONTRIBUTING.md to specify that all project documentation must be in English, including README and docstrings.
- Enhanced README.md to reference documentation guidelines and the new AGENTS.md file.
- Cleaned up .gitignore by removing unnecessary entries for cursor-related files.
- Introduced new .cursor rules for backend, frontend, project architecture, and testing to standardize development practices.

.cursor/worktrees.json

@@ -0,0 +1,5 @@
+{
+  "setup-worktree": [
+    "npm install"
+  ]
+}