Cleanup: Remove dead nav items, orphaned i18n keys, and stale ViewName entries

Student Navigation:
- Removed 6 teacher-only items from studentNavSections:
  grade-analytics, ai-tests, seating-chart, school-newsletter,
  school-transport, substitute-teacher
- Added 9 student-relevant views to studentViews:
  counseling, report-cards, student-wellness, student-career,
  school-library, announcements, peer-assessment, student-achievements,
  student-study-planner

Parent Navigation:
- Removed 2 student-only items from parentNavSections:
  student-study-planner, peer-assessment
- Added 8 parent-relevant views to parentViews:
  parents, grading, attendance, report-cards, school-library,
  student-achievements, student-career, competitions

i18n Cleanup:
- Removed 92 orphaned tablet_grading.* translation keys (47 DE + 45 EN)
  These were for features in the deleted tablet-grading-view.tsx component

ViewName Type:
- Removed 'tablet-grading', 'exam-calendar', 'school-events' from ViewName union
  (nav entries and renderView cases were already removed in previous commit)

src/lib/store.ts

@@ -41,8 +41,6 @@ export type ViewName =
   | 'parent-portal'
   | 'notification-center'
   | 'announcements'
-  | 'tablet-grading'
-  | 'exam-calendar'
   | 'student-achievements'
   | 'student-study-planner'
   | 'seating-chart'
@@ -50,7 +48,6 @@ export type ViewName =
   | 'report-cards'
   | 'data-import-export'
   | 'student-wellness'
-  | 'school-events'
   | 'substitute-teacher'
   | 'student-career'
   | 'school-newsletter'