feat: add model connectivity testing endpoints

[chenyme]

Summary

Add admin-side model testing for platform models and upstream route bindings. Platform models now support Test all, which probes all active matching upstream routes and lets admins switch between each result in the dialog. The dialog shows sanitized request/response details, latency, status code, protocol, endpoint, and supports deleting the current upstream model binding with confirmation.

Also refined the model management table UI: left-align model type tags and keep image protocol ordering stable as Images Generations before Images Edits.

Change type

• Bug fix
• Feature
• Documentation
• Refactor
• Configuration / deployment
• Security hardening
• Other

Affected areas

• Frontend / UI
• Backend / API
• Authentication / authorization
• Conversations / streaming
• Files / RAG / extraction
• Model routing / providers
• MCP / tools
• Billing / payments
• Admin console
• Deployment / Docker / configuration
• Documentation

Verification

• cd backend && go test ./...
• cd backend && make swagger
• pnpm --dir frontend lint
• pnpm --dir frontend exec tsc --noEmit
• git diff --check

Screenshots, API examples, or logs

Admin API changes:

• POST /api/v1/admin/llm/models/{id}/test-all
• POST /api/v1/admin/llm/models/{id}/test
• POST /api/v1/admin/llm/upstreams/{id}/models/{route_id}/test

Debug output is sanitized before returning to the frontend.

Configuration, migration, and compatibility notes

Configuration changes: None.

API changes: Adds platform model batch test endpoint. Existing single model and upstream route test endpoints remain available.

Database migrations: None.

Deployment changes: None.

Backward compatibility: Existing model routing and upstream configuration behavior is unchanged.

Documentation

• Documentation is not needed for this change.
• Documentation was updated.
• Documentation still needs to be updated.

Swagger docs were regenerated.

Security and privacy

• No secrets, tokens, credentials, local config, or personal data are included.
• User data access remains scoped by authenticated user context unless an admin-only path explicitly requires broader access.
• Security-sensitive behavior was reviewed, including authentication, authorization, provider routing, file processing, billing, and admin APIs where relevant.

Model test debug output redacts API keys, Authorization headers, sensitive headers, Base URL, and upstream host before returning to admins.

Checklist

• I searched existing issues and pull requests.
• Changes are focused and do not include unrelated refactors.
• Tests or static verification were run where practical.
• User-facing behavior, deployment steps, API contracts, or configuration changes are documented.
• Generated artifacts are included only when this project explicitly requires them.
• Caches, build output, .pyc files, .env files, and local storage data are not committed.