operationQueue.ts: Refactor priority levels from magic numbers to named constants

[Kingsman-99]

Description

src/operationQueue.ts uses numeric literals (e.g., 1, 5, 10) as priority levels throughout the code. These magic numbers make it hard to understand relative urgency and error-prone to add new levels. Replacing them with named constants improves readability.

Acceptance Criteria

• A OperationPriority const enum (or plain object) defines LOW = 1, NORMAL = 5, HIGH = 10 (or equivalents matching the current values)
• All numeric literals in operationQueue.ts are replaced with the named constants
• No behavior changes; only naming refactor
• Unit tests pass

Context

• Target file: src/operationQueue.ts
• Export OperationPriority so callers can use the constants too