[FEATURE]:add importing provider through auth.json

[GameCat7428]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

add importing auth.json though opencode import —file (file way)

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Can I migrate the authorization of provider with OAuth authentication? #15692: Similar request — migrating/copying auth.json credentials (OAuth tokens) to another environment, which is essentially the same use case as importing provider auth via a file.
• [FEATURE]: Support configurable auth credential file path via OPENCODE_AUTH_PATH #18562: Related feature request for configurable auth credential file path via OPENCODE_AUTH_PATH, which partially addresses the multi-environment auth portability need.

If your request is distinct from these, please clarify how it differs.