Add lessons Phase 2: schedule slots with conflict detection

Recurring weekly time slots linking instructors to lesson types.
Includes day/time overlap detection, instructor and day-of-week
filtering, and 17 new integration tests (40 total lessons tests).

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

@@ -36,3 +36,18 @@ export type LessonTypeCreateInput = z.infer<typeof LessonTypeCreateSchema>
 
 export const LessonTypeUpdateSchema = LessonTypeCreateSchema.partial()
 export type LessonTypeUpdateInput = z.infer<typeof LessonTypeUpdateSchema>
+
+// --- Schedule Slot schemas ---
+
+export const ScheduleSlotCreateSchema = z.object({
+  instructorId: z.string().uuid(),
+  lessonTypeId: z.string().uuid(),
+  dayOfWeek: z.coerce.number().int().min(0).max(6),
+  startTime: z.string().regex(/^\d{2}:\d{2}$/, 'Must be HH:MM format'),
+  room: opt(z.string().max(100)),
+  maxStudents: z.coerce.number().int().min(1).default(1),
+})
+export type ScheduleSlotCreateInput = z.infer<typeof ScheduleSlotCreateSchema>
+
+export const ScheduleSlotUpdateSchema = ScheduleSlotCreateSchema.partial()
+export type ScheduleSlotUpdateInput = z.infer<typeof ScheduleSlotUpdateSchema>