Add README

Author: bdcbqa314159

README.md

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+# CellWright
+
+Cross-platform quantitative spreadsheet built with C++20 and Dear ImGui. Designed for financial and scientific workflows: columnar storage, formula engine with dependency tracking, SIMD aggregation, embedded DuckDB SQL, plugin system, and charting via ImPlot.
+
+## Features
+
+**Core Engine**
+- Columnar storage with dense `vector<double>` and sparse non-numeric overlay
+- Recursive-descent formula parser with arena-allocated AST
+- 50+ built-in functions (math, statistics, text, logic, date)
+- Dependency graph with topological recalculation and cycle detection
+- Undo/redo (command pattern, 200 depth)
+- JSON (`.magic`) and CSV serialization
+
+**SIMD Aggregation**
+- ARM NEON / AVX2+FMA / scalar fallback
+- NaN-aware `sum`, `min`, `max`, `count`, `sum_of_squares`
+- Fast path in evaluator for single-column SUM/MIN/MAX/COUNT
+
+**Embedded SQL**
+- DuckDB v1.1.3 in-process engine (lazy init, pimpl)
+- `=SQL("SELECT ...")` formula function
+- Interactive SQL editor panel
+- Generation-based skip of redundant imports
+
+**Plugin System**
+- Three conventions: C++ (IFunction, hot-reloadable), C ABI (language-agnostic), Python (pybind11)
+- SHA-256 trust store with codesign verification (macOS)
+- Hot reload with mtime polling
+- Panel plugins (custom ImGui windows)
+
+**Arrow C Data Interface**
+- Zero-copy export of sheet data to Arrow struct arrays
+- Import Arrow record batches into sheets
+- Interop with PyArrow, Polars, and pandas
+
+**UI**
+- Spreadsheet grid with freeze panes, drag-to-move, fill handle, range selection
+- Formula bar with autocomplete, signature tooltips, reference highlighting
+- Line / bar / scatter / histogram / stacked bar charts via ImPlot
+- Find & replace, conditional formatting, per-column filtering
+- Dark / light theme, DPI awareness
+- Toast notifications, unsaved-changes guard, auto-save recovery
+- Native file dialogs, drag-and-drop plugin loading
+
+## Technology Stack
+
+| Layer | Choice |
+|-------|--------|
+| Language | C++20 |
+| UI | Dear ImGui (docking) + GLFW 3.4 + OpenGL 3 |
+| Charting | ImPlot |
+| Plugin framework | [cpp_plugin_arch](https://github.com/bdcbqa314159/cpp_plugin_arch) |
+| Python plugins | pybind11 v2.13.6 |
+| SQL engine | DuckDB v1.1.3 |
+| SIMD | ARM NEON / AVX2+FMA / scalar |
+| Interop | Arrow C Data Interface |
+| File dialogs | nativefiledialog-extended v1.2.1 |
+| Tests | Google Test v1.15.2 + pytest |
+| Build | CMake 3.20+ |
+
+## Build
+
+```bash
+# Configure (fetches all dependencies via FetchContent)
+cmake -B build -DCMAKE_BUILD_TYPE=Release
+
+# Build
+cmake --build build --parallel
+
+# Run
+./build/bin/cellwright
+```
+
+### Options
+
+| Option | Default | Description |
+|--------|---------|-------------|
+| `CELLWRIGHT_BUILD_PLUGINS` | `ON` | Build bundled plugins |
+| `CELLWRIGHT_BUILD_TESTS` | `ON` | Build test suite |
+
+### Platform dependencies
+
+**macOS** — Xcode command line tools (ships with OpenGL, Cocoa frameworks)
+
+**Linux** — install before building:
+```bash
+sudo apt-get install libgl-dev libx11-dev libxrandr-dev libxinerama-dev \
+  libxcursor-dev libxi-dev libgtk-3-dev python3-dev
+```
+
+**Windows** — Visual Studio 2022 with C++ workload
+
+## Tests
+
+```bash
+# C++ tests (254 tests across 34 suites)
+ctest --test-dir build --output-on-failure
+
+# Python tests (Arrow interop, smoke tests)
+python -m venv .venv
+source .venv/bin/activate
+pip install -r requirements.txt
+pytest tests/python -v
+```
+
+## Bundled Plugins
+
+| Plugin | Type | Functions |
+|--------|------|-----------|
+| `example_stats` | C++ IFunction | `STDEV_P` |
+| `scientific` | C++ IFunction | Trig, log, statistical |
+| `bond` | C ABI | `BOND_PRICE`, `BOND_YIELD`, `BOND_DURATION`, `BOND_CONVEXITY` |
+| `py_bond` | Python | Bond pricing via pybind11 |
+
+## License
+
+[MIT](LICENSE) -- Bernardo Cohen / deLaPatada Software