Add per-project Department management

Departments are now a customizable per-project list (standard + custom),
matching the existing custom task type/status pattern, instead of a fixed
7-value enum. They're usable directly on tasks (new field, independent of
assignee) and continue to drive team member department roles.

backend/models/project.py

@@ -2,7 +2,6 @@ from sqlalchemy import Column, Integer, String, DateTime, Date, Enum, ForeignKey
 from sqlalchemy.orm import relationship
 from sqlalchemy.sql import func
 from database import Base
-from .user import DepartmentRole
 import enum
 
 
@@ -54,6 +53,9 @@ class Project(Base):
     # Custom task statuses
     custom_task_statuses = Column(JSON, nullable=True)  # Custom task statuses for project
 
+    # Custom departments
+    custom_departments = Column(JSON, nullable=True)  # Custom departments for project (in addition to standard ones)
+
     # Submission configuration per task type
     submission_config_by_task_type = Column(JSON, nullable=True)  # Allowed file types, naming pattern, required flag per task type
 
@@ -80,7 +82,7 @@ class ProjectMember(Base):
     id = Column(Integer, primary_key=True, index=True)
     user_id = Column(Integer, ForeignKey("users.id"), nullable=False)
     project_id = Column(Integer, ForeignKey("projects.id"), nullable=False)
-    department_role = Column(Enum(DepartmentRole), nullable=True)
+    department_role = Column(String, nullable=True)  # Free-form: standard department or a project's custom department
     joined_at = Column(DateTime(timezone=True), server_default=func.now())
 
     # Relationships