FN-5914: fix mission activity counts and chronology

Keep mission activity counts accurate before event data loads and show events in chronological order.

- add persisted mission event counts to core mission summaries and dashboard mission summary types
- use the summary event count for the Activity tab preload badge instead of the currently loaded page total
- render mission activity oldest-to-newest, keep load-more prepends stable, and scroll to the latest event on initial/live updates
- extend mission store, dashboard, and MissionManager tests for event count and ordering coverage

Files changed:
 packages/core/src/__tests__/mission-store.test.ts  |  19 ++++
 packages/core/src/mission-store.ts                 |  24 ++++-
 packages/dashboard/app/api/legacy.ts               |   2 +
 .../dashboard/app/components/MissionManager.tsx    |  19 ++--
 .../components/__tests__/MissionManager.test.tsx   | 107 ++++++++++++++++-----
 packages/dashboard/app/components/mission-types.ts |   1 +
 .../dashboard/src/__tests__/mission-e2e.test.ts    |   7 +-
 7 files changed, 143 insertions(+), 36 deletions(-)

Fusion-Task-Id: FN-5914

Fusion-Task-Lineage: b3119e94-66bd-437d-bcde-d5e4e43cb29e

packages/dashboard/app/api/legacy.ts

@@ -6919,6 +6919,8 @@ export interface MissionSummary {
   completedMilestones: number;
   totalFeatures: number;
   completedFeatures: number;
+  linkedGoalCount: number;
+  eventCount: number;
   progressPercent: number;
 }