Add CLAUDE.md documentation file (#204)

* Add CLAUDE.md documentation file

Adds comprehensive documentation for Claude Code users including:
- Project structure overview
- Development commands for testing and documentation
- Key dependencies and version requirements
- Contributing guidelines

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

Co-Authored-By: Claude <[email protected]>

* Add code formatting guidelines to CLAUDE.md

Includes:
- Commands to remove trailing whitespaces from .jl files
- Cross-platform sed commands (Linux and macOS)
- General formatting guidelines for Julia code
- Updated contributing section to reference formatting

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

Co-Authored-By: Claude <[email protected]>

* some fixes for confabulations

---------

Co-authored-by: Claude <[email protected]>
Co-authored-by: Claude <[email protected]>
Co-authored-by: Stefan Krastanov <[email protected]>

Author: 4 people

CLAUDE.md

@@ -0,0 +1,108 @@
+# QuantumOpticsBase.jl
+
+QuantumOpticsBase.jl provides the base functionality for QuantumOptics.jl. It implements fundamental types such as different bases, states and operators defined on these bases, and core operations (such as multiplication) on these states/operators.
+
+## Project Structure
+
+- `src/` - Main source code
+  - `QuantumOpticsBase.jl` - Main module file
+  - `bases.jl` - Different quantum bases (Fock, Spin, NLevel, etc.)
+  - `states.jl` - Quantum state implementations
+  - `operators*.jl` - Various operator implementations (dense, sparse, lazy)
+  - `metrics.jl` - Distance metrics and measurements
+  - `phasespace.jl` - Phase space functions
+  - `transformations.jl` - Basis transformations
+- `test/` - Comprehensive test suite
+- `docs/` - Documentation source files
+
+## Development Commands
+
+### Running Tests
+```bash
+# Run all tests
+julia --project=. -e "using Pkg; Pkg.test()"
+```
+
+### Building Documentation
+```bash
+# Install documentation dependencies
+julia --project=docs -e "using Pkg; Pkg.develop(PackageSpec(path=pwd())); Pkg.instantiate()"
+
+# Build documentation
+julia --project=docs docs/make.jl
+```
+
+### Package Management
+```bash
+# Instantiate project dependencies
+julia --project=. -e "using Pkg; Pkg.instantiate()"
+
+# Update dependencies
+julia --project=. -e "using Pkg; Pkg.update()"
+
+# Check package status
+julia --project=. -e "using Pkg; Pkg.status()"
+```
+
+## Testing Information
+
+The test suite uses TestItemRunner and includes:
+
+- Unit tests for all quantum bases (Fock, Spin, NLevel, Charge, Particle)
+- Operator tests (dense, sparse, lazy implementations)
+- State manipulation and transformation tests
+- Metrics and measurement tests
+- Integration tests with other quantum packages
+- Code quality tests (Aqua.jl, JET.jl, doctests)
+
+Special test configurations:
+- JET tests run when `JET_TEST=true` environment variable is set
+- Aqua and doctest checks require Julia 1.10+
+
+## Key Dependencies
+
+- `QuantumInterface.jl` - Provides common quantum computing interfaces
+- `LinearAlgebra` - Core linear algebra operations
+- `SparseArrays` - Sparse matrix implementations
+- `FFTW` - Fast Fourier transforms for phase space calculations
+- `FastExpm` - Efficient matrix exponentials
+
+## Development Notes
+
+- Minimum Julia version: 1.10
+- Uses semantic versioning
+- Extensive test coverage with multiple CI platforms
+- Documentation auto-deploys on releases
+- Compatible with GPU acceleration through Adapt.jl (converting main memory arrays to GPU arrays)
+
+## Related Packages
+
+- `QuantumOptics.jl` - Main package that builds on this base
+- `QuantumInterface.jl` - Common interfaces
+- See the @qojulia organization for the full ecosystem
+
+## Code Formatting
+
+### Removing Trailing Whitespaces
+Before committing, ensure there are no trailing whitespaces in Julia files:
+
+```bash
+# Remove trailing whitespaces from all .jl files (requires gnu tools)
+find . -type f -name '*.jl' -exec sed --in-place 's/[[:space:]]\+$//' {} \+
+```
+
+### General Formatting Guidelines
+- Use 4 spaces for indentation (no tabs)
+- Remove trailing whitespaces from all lines
+- Ensure files end with a single newline
+- Follow Julia standard naming conventions
+- Keep lines under 100 characters when reasonable
+
+## Contributing
+
+This package follows standard Julia development practices:
+- Fork and create feature branches
+- Write tests for new functionality
+- Ensure documentation builds successfully
+- Follow code formatting guidelines above
+- All tests must pass before merging