feat(backend): subtask category support (schema, validation, sync, routes)

backend/src/db/schema.ts

@@ -44,6 +44,7 @@ export const tasks = pgTable('tasks', {
   id: text('id').primaryKey(),
   userId: text('user_id').notNull().references(() => users.id, { onDelete: 'cascade' }),
   categoryId: text('category_id').references(() => categories.id, { onDelete: 'cascade' }),
+  tags: text('tags').notNull().default(''),
   title: text('title').notNull(),
   description: text('description').notNull().default(''),
   priority: text('priority', { enum: ['none', 'low', 'medium', 'high', 'critical'] }).notNull().default('none'),
@@ -84,6 +85,7 @@ export const subtasks = pgTable('subtasks', {
   userId: text('user_id').notNull().references(() => users.id, { onDelete: 'cascade' }),
   taskId: text('task_id').notNull().references(() => tasks.id, { onDelete: 'cascade' }),
   parentSubtaskId: text('parent_subtask_id').references((): AnyPgColumn => subtasks.id, { onDelete: 'cascade' }),
+  categoryId: text('category_id').references(() => categories.id, { onDelete: 'set null' }),
   title: text('title').notNull(),
   description: text('description').notNull().default(''),
   priority: text('priority', { enum: ['none', 'low', 'medium', 'high', 'critical'] }).notNull().default('none'),