Add route description column to operation table

[gandalf-at-lerian]

Context

The operation table currently stores the route_code from the associated operation route, but does not persist the route_description. This limits the ability to provide meaningful context about operations without joining back to the operation route table.

Goal

Add a route_description column to the operation table, populated during transaction processing alongside route_code.

Acceptance Criteria

• New route_description column added to the operation table (migration)
• route_description is persisted when creating operations
• route_description is returned in operation query responses
• Existing operations without route_description are not affected (nullable column)