feat: support an override option for imported objects

[Hacks4Snacks]

What changed

• Added Import recovery copy in Studio and VS Code for .tm7 files with unattached or cross-page flow endpoints.
• Recovery creates a separate JSON draft, omitting broken flows and scoped threats with explicit loss warnings.
• Original files remain untouched. Other validation errors and safety limits remain blocking.

Why

Allow usable content from imperfect threat models to be imported without silently discarding data or disabling validation.