Add activated-team welcome screen and auto-redirect

[neerpatel]

Parent: #4

Summary

Build the returning-player flow that shows the team identity briefly before redirecting into the active race experience.

Acceptance Criteria

• Players joining an activated team see a branded welcome state for a short fixed interval.
• The welcome view uses the existing team car and team name data.
• The flow automatically redirects to the Race Hub without extra user input.

[neerpatel]

Review pass on April 10, 2026:

This issue remains open. There is currently no activated-team welcome/interstitial screen in the app.

Current behavior:

• Active users are routed directly to /race-hub from the login flow.
• I did not find a timed branded intermediate view that shows team logo/name before redirect.

Leaving open until the welcome-state screen and timed redirect are implemented.

[neerpatel]

Added supporting system/player feed work for onboarding visibility in Race Hub:\n- #86 (team activity event log + API)\n- #87 (Race Hub running team activity feed)\n\nThis keeps activated-team entry context visible in the ongoing team activity timeline.