Add pc/ — PyInstaller build scripts, .ico icon, and README

pc/build.bat

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+@echo off
+cd /d "%~dp0"
+echo Installing PyInstaller...
+pip install pyinstaller
+
+echo Building Kanjin.exe...
+REM --onefile: single executable
+REM --name: output filename
+REM --icon: application icon
+REM --distpath=. : place .exe in this directory (pc/)
+REM --workpath: temp build folder (cleaned up)
+python -m PyInstaller --onefile --name Kanjin --icon=kanjin.ico --distpath=. --workpath=build_temp ..\main.py
+
+echo Cleaning up...
+rd /s /q build_temp __pycache__ 2>nul
+del Kanjin.spec 2>nul
+
+echo.
+echo Done! Deliver pc\Kanjin.exe to players.
+pause