feat: Add Windows compatibility, PyInstaller build setup, and custom icon

- Add Windows LibreOffice detection fallback for soffice path
  - Check standard install locations (%PROGRAMFILES%, %PROGRAMFILES(X86)%)
  - Graceful fallback with clear error messages

- Add PyInstaller build infrastructure
  - build/ccma.spec: PyInstaller configuration with icon generation
  - build/build.ps1: Automated build script for standalone exe
  - main.py: Entry point for PyInstaller
  - Supports versioning and architecture tagging

- Create custom CCMA icon
  - Person + Gear symbol representing member administration
  - Cyan/White/Orange color scheme
  - Auto-converts PNG to ICO during build

- Update documentation
  - README: Windows PowerShell setup instructions
  - README: Linux/macOS bash setup instructions
  - README: Standalone executable build guide
  - pyproject.toml: Add 'build' extra with pyinstaller+pillow

- Add regression tests
  - Test office executable detection and Windows fallback
  - Verify all tests pass (80 passed)

README.md

@@ -12,6 +12,29 @@ Requires Python 3.11+ with Tk support.
 PDF generation from document templates additionally requires LibreOffice or
 OpenOffice with a `soffice` command available on the system.
 
+### Windows (PowerShell)
+
+```powershell
+python -m venv .venv
+.\.venv\Scripts\python.exe -m pip install -r requirements.txt
+.\.venv\Scripts\ccma.exe
+```
+
+For development tools and tests, install the `dev` extra as well:
+
+```powershell
+.\.venv\Scripts\python.exe -m pip install -e .[dev]
+```
+
+Alternatively, without installation:
+
+```powershell
+$env:PYTHONPATH = "src"
+.\.venv\Scripts\python.exe -m ccma
+```
+
+### Linux/macOS
+
 ```bash
 python -m venv .venv
 .venv/bin/pip install -r requirements.txt
@@ -30,6 +53,32 @@ Alternatively, without installation:
 PYTHONPATH=src python -m ccma
 ```
 
+If LibreOffice is installed on Windows but `soffice` is not in `PATH`, CCMA
+also checks the default install locations under `%PROGRAMFILES%` and
+`%PROGRAMFILES(X86)%`.
+
+## Building standalone executables
+
+To bundle CCMA into a single-file Windows executable with PyInstaller, use the
+build script in the `build/` directory:
+
+### Windows standalone build
+
+```powershell
+cd build
+.\build.ps1
+```
+
+This creates two executables in the `dist/` directory:
+- `ccma.exe` (generic)
+- `ccma-<version>-windows-<arch>.exe` (version and architecture-specific, e.g. `ccma-0.1.0-windows-amd64.exe`)
+
+The build script automatically:
+- Creates a venv if missing
+- Installs dependencies and PyInstaller
+- Generates a Windows icon from the splash image
+- Runs PyInstaller to bundle the application
+
 On first start, select or create the central member-store directory. The
 `VERSION` file is the single source for application and package versions.