Add CLAUDE.md guidance file

Author: lefticus

CLAUDE.md

@@ -0,0 +1,19 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build Commands
+- Configure: `cmake -S . -B ./build -G Ninja` or `cmake . --preset <configure-preset>` (CMake 3.21+)
+- Build: `cmake --build ./build`
+- Run tests: `cd ./build && ctest -C Debug && cd ..`
+- Run specific test: `cd ./build && ./test/tests "[test name]" && cd ..`
+- Static analysis: Enable with `-Dinfiz_ENABLE_CLANG_TIDY=ON` or `-Dinfiz_ENABLE_CPPCHECK=ON`
+
+## Code Style Guidelines
+- Standard: C++23
+- Formatting: 2-space indentation, 120 char line limit, braces on new lines for functions/classes
+- Naming: Classes=PascalCase, Methods/Variables=camelCase, Constants/Enums=UPPER_CASE
+- Error handling: Use exceptions with descriptive messages, lambda error handlers
+- Features: Use `constexpr`, `consteval`, `[[nodiscard]]`, concepts, format strings
+- Headers: Include guards with `INFIZ_NAME_H` format, sort includes logically
+- Functions: Prefer pure functions marked with `[[nodiscard]]` where possible