[Project] Add Claude Code and Cursor AI assistant configuration

[Project] Add Claude Code and Cursor AI assistant configuration

Add comprehensive configuration for AI development assistants:

.claude/ - Claude Code configuration:
- project_context.md: Project rules, code style, commit format, build system
- commands/: Custom slash commands for development workflow
  - build, test, build-and-test: Build and testing commands
  - check-code, format-code, test-lua: Code quality commands
  - prepare-commit, review-pr, create-release: Git workflow commands
- README.md: Documentation for all commands and features

.cursor/rules/ - Cursor rules:
- build-and-test.mdc: Build system and testing workflow documentation

Features:
- Automated code quality checks (luacheck, clang-format)
- Build system integration (ninja in ~/rspamd.build)
- Unit test execution (C/C++ and Lua tests)
- Commit message validation and formatting
- PR review assistance
- Release process automation

This enables AI assistants to follow Rspamd development practices
and automate common development tasks.