iEduPortal Stage 113 — Main Pages Dashboard Foundation

Introduces the first production-facing main page: a responsive, role-aware dashboard shell using the existing authenticated API and academic context layers. Adds dashboard summary cards, capability-aware main-page navigation, account/session state, and mobile-friendly layout. No database migration. Existing Stage 112 scheduling/PWA infrastructure is preserved.
Deployment-safe checker: /stage113.php
