chore: prepare Frontend 1.9.0

[Priveetee]

Summary

• Release the current Frontend line as TypeType 1.9.0.
• Add desktop subscription-group management and improve BiliBili session, Takeout import, and watch/player flows.
• Add channel-avatar loading and retry states, and remove the duplicate NicoNico service entry.

Production behavior

• Updates the web client for subscription groups, portability imports, BiliBili sessions, and SABR/watch playback controls.

Deployment requirements

• Deploy with the matching TypeType 1.9.0 Server APIs and the Frontend image built from the merged revision.

Runtime verification

• The main-branch Docker workflow completed successfully.
• Production browser verification remains pending the rollout.

Tests

• Pull request CI checks passed.

Rollback

• Restore the previous Frontend image reference together with its compatible Server API revision.