Update README for accuracy and completeness

[Copilot]

README didn't reflect the full project state — missing Python version coverage, file layout, and contributor guidance on the dialog format.

• Python badge: 3.12 → 3.10 | 3.11 | 3.12 to match CI matrix
• Intro: Replaced single-line description with backend + interface summary tables
• Prerequisites: New section — Python 3.10+, pip, optional OpenAI key / Docker
• Project Structure: New section — annotated file tree
• CI/CD: Added multi-version testing detail and coverage artifact mention
• Contributing: Documented dialog.csv format for adding patterns:

dialog_id,line_id,text
8,1,What is Python?
8,2,Python is a popular programming language!

• ToC: Updated with new sections

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• api.kaggle.com
  • Triggering command: /usr/bin/python python -m pytest test_chatbot.py -v --tb=short (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.