[johanbeytell1]

Summary

Fixes the silent contact overwrite reported in #18.

Beginner/14_address_book.py previously did contacts[name] = {...} unconditionally, so adding an existing name destroyed the saved contact with no warning. Adding a duplicate name now shows the existing contact's details and asks what to do:

1. Overwrite the existing contact
2. Keep both — save the new contact under an incremented name: Rani (2), Rani (3), ...
3. Cancel — nothing is saved

Changes

• Added next_available_name() to find the first free numbered suffix, handling names that already have one (e.g. adding Rani (2) suggests Rani (3)).
• Added resolve_name() for duplicate handling; an existing contact is replaced only after explicit confirmation.
• Phone/email are requested after the duplicate is resolved, so cancelling doesn't waste typing.
• Trim whitespace from entered names and reject empty names.
• README.md: noted the change under Latest Changes, added a step about checking for an existing name, and added Tip 3 explaining never to overwrite a contact silently — with credit to @SVarnavi06 for reporting the bug.

Testing

Ran the script against a real contacts.json and verified all three paths:

• Overwrite: original entry replaced as confirmed.
• Keep both: saved as rani (2), then rani (3) on the next duplicate.
• Cancel: no changes written to disk.

Closes #18.