Add comprehensive barbershop management desktop app

[UncleFisl]

Summary

• create a standalone Tkinter desktop application with themed dashboard, booking form, appointment grid, and shortcut-enabled actions
• implement SQLite-backed appointment workflow with validation, conflict checks, loyalty accounting, and automatic session completion
• add management and reporting windows for sessions, customers, barbers, services, daily metrics, monthly analytics, and shop settings

Testing

• python -m compileall barbershop.py

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Codex Task