RTDB import safety: make replace optional + warn/prompt before destructive import

[omer-ayhan]

Feature Description

RTDB import currently replaces data at the target path by default. Make destructive “replace” behavior optional, and add a clear warning prompt to prevent accidental data loss.

Proposed CLI / UX

• Add a flag:
  • --replace (explicit destructive overwrite)
• Add prompt behavior:
  • If --replace is used, prompt the user to confirm unless --force/--yes is provided.
• Default behavior (when --replace is not set):
  • should be non-destructive (merge/update) — define exact semantics in docs.

Acceptance Criteria

• Replace is not accidental:
  • --replace required for destructive overwrite
  • confirmation prompt shown unless --force/--yes
• Non-replace mode performs documented merge/update semantics.
• Docs updated with warnings + examples.
• Tests cover:
  • replace vs merge behavior
  • prompt shown / prompt bypassed

Additional Context

Implementation Subtasks

1. Flag design (--replace, --force/--yes)
2. Prompt and messaging
3. Implement set() vs update() behavior
4. Docs + tests