Self-hosted Label Studio is unusable offline (hard frontend dependency on internet)

Label Studio version: 1.21.0
Image: heartexlabs/label-studio (official Docker image)
Deployment: self-hosted with local PostgreSQL
Environment: offline / air-gapped

Expected behavior:
A self-hosted Label Studio instance must work fully offline when all data,
database, and services are local and analytics are disabled.

Actual behavior:
When the machine has no internet connection:
- UI loads but project pages hang indefinitely
- Backend APIs respond normally (200 OK)
- No pending requests, no visible errors
- The moment internet connectivity is restored, the UI immediately works

This makes Label Studio unusable offline.

Disabled configuration (confirmed at runtime):
- COLLECT_ANALYTICS=0
- SENTRY_DSN=
- FRONTEND_SENTRY_DSN=

No references to Sentry or Google Analytics appear in:
- rendered HTML
- served JS bundles

Nevertheless, the frontend still blocks without internet access.

Why this is critical:
- Breaks air-gapped and regulated deployments
- Violates expectations of self-hosted software
- Creates a hidden online dependency without warning or documentation

This is not a configuration issue.
It is a frontend architecture problem: the UI implicitly depends on external
connectivity even in self-hosted mode.

Request:
Please remove all implicit frontend dependencies on external services or
explicitly document that Label Studio cannot run offline.