feat: add lead-only status change rule for boards and update related logic

backend/app/schemas/boards.py

@@ -32,6 +32,7 @@ class BoardBase(SQLModel):
     require_approval_for_done: bool = True
     require_review_before_done: bool = False
     block_status_changes_with_pending_approval: bool = False
+    only_lead_can_change_status: bool = False
 
 
 class BoardCreate(BoardBase):
@@ -74,6 +75,7 @@ class BoardUpdate(SQLModel):
     require_approval_for_done: bool | None = None
     require_review_before_done: bool | None = None
     block_status_changes_with_pending_approval: bool | None = None
+    only_lead_can_change_status: bool | None = None
 
     @model_validator(mode="after")
     def validate_gateway_id(self) -> Self: