feat: add assigneeId/assigneeName to tasks schema and API

- Added assignee_id and assignee_name columns to tasks table
- PATCH /api/tasks/:id now accepts assigneeId and assigneeName
- db:push on startup will auto-migrate the columns

backend/src/db/schema.ts

@@ -47,6 +47,8 @@ export const tasks = pgTable("tasks", {
   status: taskStatusEnum("status").notNull().default("queued"),
   priority: taskPriorityEnum("priority").notNull().default("medium"),
   position: integer("position").notNull().default(0),
+  assigneeId: text("assignee_id"),
+  assigneeName: text("assignee_name"),
   progressNotes: jsonb("progress_notes").$type<ProgressNote[]>().default([]),
   createdAt: timestamp("created_at", { withTimezone: true }).defaultNow().notNull(),
   updatedAt: timestamp("updated_at", { withTimezone: true }).defaultNow().notNull(),