docs: add laundry-desk design spec (M0)

洗衣店柜台管理系统的初始设计文档。单店单机 Electron + SQLite，
Apple HIG UI，4 期交付（M1 基础 → M2 收款统计 → M3 拍照打印
→ M4 员工短信）。实现交给 Gemini，Claude 守门禁，Codex 二审。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitignore

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+# dependencies
+node_modules/
+.pnpm-store/
+
+# build output
+dist/
+out/
+build/
+release/
+*.asar
+
+# packaged binaries
+*.exe
+*.dmg
+*.pkg
+*.zip
+*.blockmap
+
+# env / secrets
+.env
+.env.*
+!.env.example
+
+# logs
+*.log
+npm-debug.log*
+pnpm-debug.log*
+yarn-debug.log*
+
+# OS
+.DS_Store
+Thumbs.db
+Desktop.ini
+
+# editors
+.vscode/*
+!.vscode/extensions.json
+!.vscode/settings.example.json
+.idea/
+*.swp
+*.swo
+
+# runtime (Electron userData during dev)
+userData/
+backups/
+photos/
+*.sqlite
+*.sqlite-journal
+*.db
+*.db-journal
+*.db-shm
+*.db-wal