Fix quickstart panel formatting and tests

[cybergoOod-KMT]

Summary

This PR adds and hardens a beginner-friendly quickstart panel and installer helpers for tabdeal-python.

The change is intentionally narrow and keeps the existing SDK API unchanged.

Changes

• Adds .env.example with placeholders only.
• Adds Linux and Windows installer helpers.
• Adds a safe local quickstart helper module.
• Adds a Tkinter-based quickstart panel.
• Adds python -m tabdeal entrypoint.
• Adds unit tests for quickstart behavior.
• Updates README with minimal quickstart usage and safety notes.

Safety

• No real trading is performed by the panel.
• API secrets are masked in the panel.
• API secrets are not logged or printed.
• Generated examples use environment variables and never embed live secrets.
• Existing generated examples are not overwritten automatically.
• Config is stored only in the local per-user app config path.

Validation

python -m compileall tabdeal tests