Begin pilot program for Claude code reviews with initial system prompt (#6371)

* Rough draft of a markdown file to give context to Claude.

CLAUDE.md

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+# Bitwarden Server - Claude Code Configuration
+
+## Critical Rules
+
+- **NEVER** edit: `/bin/`, `/obj/`, `/.git/`, `/.vs/`, `/packages/`, generated migration files
+- **Security First**: All code changes must prioritize cryptographic integrity and data protection
+- **Test Coverage**: New features require xUnit unit tests with NSubstitute mocking
+- **Check CODEOWNERS requirements**: The repo has a `.github/CODEOWNERS` file to define team ownership for different parts of the codebase. Respect that code owners have final authority over their designated areas
+
+## Project Context
+
+**Architecture**: CQRS pattern with feature-based organization
+**Framework**: .NET 8.0, ASP.NET Core
+**Database**: SQL Server primary, EF Core supports PostgreSQL, MySQL/MariaDB, SQLite
+**Testing**: xUnit, NSubstitute
+**Container**: Docker, Docker Compose, Kubernetes/Helm deployable
+
+## Development Standards
+
+### CQRS Pattern
+
+- Commands: `/src/Core/[Feature]/Commands/`
+- Queries: `/src/Core/[Feature]/Queries/`
+- Handlers implement `ICommandHandler<T>` or `IQueryHandler<T>`
+
+### API Conventions
+
+- RESTful endpoints with standard HTTP status codes
+- Consistent error response: `{ "error": { "message": "..." } }`
+- Pagination: `?skip=0&take=25`
+- API versioning: `/api/v1/`
+
+### Database Migrations
+
+- **SQL Server**: Manual scripts in `/util/Migrator/DbScripts/`
+- **Other DBs**: EF Core migrations via `pwsh ef_migrate.ps1`
+
+## Security Requirements
+
+- **Compliance**: SOC 2 Type II, SOC 3, HIPAA, ISO 27001, GDPR, CCPA
+- **Principles**: Zero-knowledge, end-to-end encryption, secure defaults
+- **Validation**: Input sanitization, parameterized queries, rate limiting
+- **Logging**: Structured logs, no PII/sensitive data in logs
+
+## Code Review Checklist
+
+- Security impact assessed
+- xUnit tests added/updated
+- Performance impact considered
+- Error handling implemented
+- Breaking changes documented
+- CI passes: build, test, lint
+
+## References
+
+- [Architecture](https://contributing.bitwarden.com/architecture/server/)
+- [Contributing Guidelines](https://contributing.bitwarden.com/contributing/)
+- [Setup Guide](https://contributing.bitwarden.com/getting-started/server/guide/)
+- [Code Style](https://contributing.bitwarden.com/contributing/code-style/)
+- [Bitwarden security whitepaper](https://bitwarden.com/help/bitwarden-security-white-paper/)
+- [Bitwarden security definitions](https://contributing.bitwarden.com/architecture/security/definitions)