P0: Add Mission Control integration regression suite

[bleuropa]

Summary

Create integration test suite for Mission Control regressions: counts, lifecycle cards, reply flow, and expansion persistence.

Context

Current tests cover component rendering but miss multi-surface consistency and nested-team behavior that caused user-visible regressions.

Suggested test areas:

• workspace_live event pipeline
• nested team aggregation
• reply targeting
• expansion persistence under update churn

Dependencies

• Depends on P0: Guard Manager.list_agents/1 against keeper entries #89
• Depends on P1: Unify Mission Control agent counts across all surfaces #93
• Depends on P1: Add missing :task_created lifecycle event to activity feed #94
• Depends on P1: Persist activity card expand/collapse state across updates #96
• Depends on P0: Add discoverable per-agent reply controls in Mission Control #97

Acceptance Criteria

• Automated tests validate consistent agent counts across header/roster/dashboard.
• Tests cover task_created + assignment lifecycle rendering.
• Tests cover reply target routing in nested teams.
• Tests validate card expansion state survives parent updates.
• Suite runs in CI and blocks regressions.