APPS-3853 Fix incorrect streak display

[XanderZhu]

YouTrack task: APPS-3853

Description List:

• Fix incorrect streak display caused by calculating user streak counters from the limited user-activities pins array.
• Use GET /api/user-activity-summaries/{user_id} as described in docs/APPS-3853.md.
• Display current streak from recent_strike, max streak from max_strike, and active/continue state from solved_today > 0.
• Keep pins for activity graph data and leave the old user-activities endpoint/helpers for compatibility.
• Update profile activities, home streak, post-login streak dialog, and streak notifications.
• Add unit coverage for profile activity mapping, long streak summary consumers, and streak notification branching.

Testing:

• ./gradlew :app:compileDebugUnitTestKotlin - passed.
• ./gradlew :app:testDebugUnitTest - passed.