Add Phase 7: grade history and session-plan item linking

- New tables: lesson_plan_item_grade_history (append-only), lesson_session_plan_item
- Grading an item updates current_grade_value and creates immutable history record
- Grading a not_started item auto-transitions it to in_progress
- Linking items to a session also auto-transitions not_started items
- Link operation is idempotent — re-linking same items produces no duplicates
- Endpoints: POST/GET /lesson-plan-items/:id/grades, GET /lesson-plan-items/:id/grade-history
- Endpoints: POST/GET /lesson-sessions/:id/plan-items
- 8 new integration tests

packages/shared/src/schemas/lessons.schema.ts

@@ -199,3 +199,20 @@ export const LessonPlanItemUpdateSchema = z.object({
   sortOrder: z.coerce.number().int().optional(),
 })
 export type LessonPlanItemUpdateInput = z.infer<typeof LessonPlanItemUpdateSchema>
+
+// --- Grade History schemas ---
+
+export const GradeCreateSchema = z.object({
+  gradingScaleId: opt(z.string().uuid()),
+  gradeValue: z.string().min(1).max(50),
+  sessionId: opt(z.string().uuid()),
+  notes: opt(z.string()),
+})
+export type GradeCreateInput = z.infer<typeof GradeCreateSchema>
+
+// --- Session Plan Items schemas ---
+
+export const SessionPlanItemsSchema = z.object({
+  lessonPlanItemIds: z.array(z.string().uuid()).min(1),
+})
+export type SessionPlanItemsInput = z.infer<typeof SessionPlanItemsSchema>