build: add minimal developer setup doc

Author: stacknil

docs/dev-setup.md

@@ -0,0 +1,67 @@
+# Developer Setup
+
+This note is for contributors working in a fresh local environment. It keeps the setup small and mirrors the repository's existing CMake and CTest flow.
+
+## Required Tools
+
+- CMake 3.21 or newer for the shared presets in `CMakePresets.json`
+- CMake 3.20 or newer for the manual fallback flow
+- A C++20 compiler
+  - Windows: Visual Studio 2022 or Build Tools 2022 with the MSVC v143 toolset
+  - Linux: `g++` 10+ or `clang++` 14+ plus `make` or `ninja`
+- Git for normal contribution flow
+
+## Quick Start With Presets
+
+`CMakePresets.json` includes two repeatable local entry points:
+
+- `dev-debug`: default local iteration build with tests enabled
+- `ci-release`: release build intended to mirror the GitHub Actions CI flags
+
+Local debug iteration:
+
+```bash
+cmake --preset dev-debug
+cmake --build --preset dev-debug
+ctest --preset dev-debug
+```
+
+Local CI-style validation:
+
+```bash
+cmake --preset ci-release
+cmake --build --preset ci-release
+ctest --preset ci-release
+```
+
+## Manual Fallback
+
+If you do not want to use presets, or if your local CMake is 3.20 but not 3.21+, the equivalent manual flow is:
+
+```bash
+cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -D BUILD_TESTING=ON
+cmake --build build
+ctest --test-dir build --output-on-failure
+```
+
+## Windows Notes
+
+- Run from a Developer PowerShell for Visual Studio 2022, an x64 Native Tools prompt, or another shell where the MSVC toolchain is already available.
+- If `cmake` is missing from `PATH`, install either the Visual Studio C++ workload with CMake support or a standalone Kitware CMake package, then reopen the shell.
+- Visual Studio generators are multi-config, so the presets set `Debug` or `Release` again at build and test time for consistency.
+
+## Linux Notes
+
+- A small Ubuntu/Debian-style setup is usually enough:
+
+```bash
+sudo apt install cmake g++ make
+```
+
+- If you prefer Clang, configure manually with `-D CMAKE_CXX_COMPILER=clang++` or create a local user preset.
+
+## Expected Local Outputs
+
+- Build directories under `build/dev-debug` or `build/ci-release`
+- Test runs for `parser`, `detector`, and `cli`
+- `compile_commands.json` in the debug build directory when the selected generator supports it