Merge exams grading into homework

Redirect /teacher/exams/grading* to /teacher/homework/submissions; remove exam grading UI/actions/data-access; add homework student workflow and update design docs.

src/shared/db/schema.ts

@@ -269,6 +269,127 @@ export const submissionAnswers = mysqlTable("submission_answers", {
   submissionIdx: index("submission_idx").on(table.submissionId),
 }));
 
+export const homeworkAssignments = mysqlTable("homework_assignments", {
+  id: id("id").primaryKey(),
+  sourceExamId: varchar("source_exam_id", { length: 128 }).notNull(),
+  title: varchar("title", { length: 255 }).notNull(),
+  description: text("description"),
+  structure: json("structure"),
+  status: varchar("status", { length: 50 }).default("draft"),
+  creatorId: varchar("creator_id", { length: 128 }).notNull(),
+  availableAt: timestamp("available_at"),
+  dueAt: timestamp("due_at"),
+  allowLate: boolean("allow_late").default(false).notNull(),
+  lateDueAt: timestamp("late_due_at"),
+  maxAttempts: int("max_attempts").default(1).notNull(),
+  createdAt: timestamp("created_at").defaultNow().notNull(),
+  updatedAt: timestamp("updated_at").defaultNow().onUpdateNow().notNull(),
+}, (table) => ({
+  creatorIdx: index("hw_assignment_creator_idx").on(table.creatorId),
+  sourceExamIdx: index("hw_assignment_source_exam_idx").on(table.sourceExamId),
+  statusIdx: index("hw_assignment_status_idx").on(table.status),
+  sourceExamFk: foreignKey({
+    columns: [table.sourceExamId],
+    foreignColumns: [exams.id],
+    name: "hw_asg_exam_fk",
+  }).onDelete("cascade"),
+  creatorFk: foreignKey({
+    columns: [table.creatorId],
+    foreignColumns: [users.id],
+    name: "hw_asg_creator_fk",
+  }).onDelete("cascade"),
+}));
+
+export const homeworkAssignmentQuestions = mysqlTable("homework_assignment_questions", {
+  assignmentId: varchar("assignment_id", { length: 128 }).notNull(),
+  questionId: varchar("question_id", { length: 128 }).notNull(),
+  score: int("score").default(0),
+  order: int("order").default(0),
+}, (table) => ({
+  pk: primaryKey({ columns: [table.assignmentId, table.questionId] }),
+  assignmentIdx: index("hw_assignment_questions_assignment_idx").on(table.assignmentId),
+  assignmentFk: foreignKey({
+    columns: [table.assignmentId],
+    foreignColumns: [homeworkAssignments.id],
+    name: "hw_aq_a_fk",
+  }).onDelete("cascade"),
+  questionFk: foreignKey({
+    columns: [table.questionId],
+    foreignColumns: [questions.id],
+    name: "hw_aq_q_fk",
+  }).onDelete("cascade"),
+}));
+
+export const homeworkAssignmentTargets = mysqlTable("homework_assignment_targets", {
+  assignmentId: varchar("assignment_id", { length: 128 }).notNull(),
+  studentId: varchar("student_id", { length: 128 }).notNull(),
+  createdAt: timestamp("created_at").defaultNow().notNull(),
+}, (table) => ({
+  pk: primaryKey({ columns: [table.assignmentId, table.studentId] }),
+  assignmentIdx: index("hw_assignment_targets_assignment_idx").on(table.assignmentId),
+  studentIdx: index("hw_assignment_targets_student_idx").on(table.studentId),
+  assignmentFk: foreignKey({
+    columns: [table.assignmentId],
+    foreignColumns: [homeworkAssignments.id],
+    name: "hw_at_a_fk",
+  }).onDelete("cascade"),
+  studentFk: foreignKey({
+    columns: [table.studentId],
+    foreignColumns: [users.id],
+    name: "hw_at_s_fk",
+  }).onDelete("cascade"),
+}));
+
+export const homeworkSubmissions = mysqlTable("homework_submissions", {
+  id: id("id").primaryKey(),
+  assignmentId: varchar("assignment_id", { length: 128 }).notNull(),
+  studentId: varchar("student_id", { length: 128 }).notNull(),
+  attemptNo: int("attempt_no").default(1).notNull(),
+  score: int("score"),
+  status: varchar("status", { length: 50 }).default("started"),
+  startedAt: timestamp("started_at").defaultNow().notNull(),
+  submittedAt: timestamp("submitted_at"),
+  isLate: boolean("is_late").default(false).notNull(),
+  createdAt: timestamp("created_at").defaultNow().notNull(),
+  updatedAt: timestamp("updated_at").defaultNow().onUpdateNow().notNull(),
+}, (table) => ({
+  assignmentStudentIdx: index("hw_assignment_student_idx").on(table.assignmentId, table.studentId),
+  assignmentFk: foreignKey({
+    columns: [table.assignmentId],
+    foreignColumns: [homeworkAssignments.id],
+    name: "hw_sub_a_fk",
+  }).onDelete("cascade"),
+  studentFk: foreignKey({
+    columns: [table.studentId],
+    foreignColumns: [users.id],
+    name: "hw_sub_student_fk",
+  }).onDelete("cascade"),
+}));
+
+export const homeworkAnswers = mysqlTable("homework_answers", {
+  id: id("id").primaryKey(),
+  submissionId: varchar("submission_id", { length: 128 }).notNull(),
+  questionId: varchar("question_id", { length: 128 }).notNull(),
+  answerContent: json("answer_content"),
+  score: int("score"),
+  feedback: text("feedback"),
+  createdAt: timestamp("created_at").defaultNow().notNull(),
+  updatedAt: timestamp("updated_at").defaultNow().onUpdateNow().notNull(),
+}, (table) => ({
+  submissionIdx: index("hw_answer_submission_idx").on(table.submissionId),
+  submissionQuestionIdx: index("hw_answer_submission_question_idx").on(table.submissionId, table.questionId),
+  submissionFk: foreignKey({
+    columns: [table.submissionId],
+    foreignColumns: [homeworkSubmissions.id],
+    name: "hw_ans_sub_fk",
+  }).onDelete("cascade"),
+  questionFk: foreignKey({
+    columns: [table.questionId],
+    foreignColumns: [questions.id],
+    name: "hw_ans_q_fk",
+  }),
+}));
+
 // Re-export old courses table if needed or deprecate it. 
 // Assuming we are replacing the old simple schema with this robust one.
 // But if there were existing tables, we might keep them or comment them out.