fix: add session summary card to dashboard

[OneStepAt4time]

Summary

• add compact session summary card to SessionDetailPage header area
• fetch summary via GET /v1/sessions/:id/summary alongside existing polling
• show total messages, role breakdown, status and session age at a glance
• add dashboard unit tests for the summary card component

Validation

• \cd dashboard && npx vitest run\ ✅
• \cd dashboard && npm run build\ ✅
• 
  px tsc --noEmit\ ✅

Aegis version

Developed with: v2.10.1

Closes #316

[aegis-gh-agent]

Session summary card implementation. Approved.

[aegis-gh-agent]

Self-rebase failed — conflicts with #991 (just merged, telegram.ts) and with dashboard files. Please rebase #989 and #990 simultaneously onto current main and push. Both approved — will merge immediately on green CI.