SI-2: Migrate whitelist context to contract-first architecture

[josecelano]

Subissue of EPIC #1938 — REST API Contract-First Migration

Problem

The whitelist context (add_torrent_to_whitelist, remove_torrent_from_whitelist, reload_whitelist handlers) in axum-rest-api-server currently calls tracker_core::whitelist::manager::WhitelistManager directly. It has no protocol DTOs, no port trait, and no use-case service.

Per the contract-first architecture, the migration needs a whitelist command port, a runtime adapter wrapping WhitelistManager, and rewired Axum handlers.

Scope

• Define WhitelistCommandPort trait in rest-api-application/src/ports/
• Implement WhitelistApiService use-case in rest-api-application/src/use_cases/
• Implement TrackerWhitelistAdapter in rest-api-runtime-adapter/src/adapters/
• Rewire Axum handlers to dispatch through use-case
• Update Axum state/routes to wire the new adapter

Checklist

• WhitelistCommandPort trait defined in rest-api-application
• WhitelistApiService use-case implemented
• TrackerWhitelistAdapter implemented in rest-api-runtime-adapter
• Axum handlers dispatch through use-case instead of direct WhitelistManager
• Pre-commit checks pass
• Pre-push checks pass

[josecelano]

Implemented via #1947