refactor(apple): type core event phase/kind/direction as enums

Replaces the stringly-typed transfer-event phase/kind/direction values
throughout the progress-derivation logic with EventPhase, EventKind and
EventDirection enums (String-backed to match the core's wire values).

CoreEventModel keeps the raw wire strings as a faithful boundary DTO but
exposes typed eventPhase/eventKind/eventDirection accessors; all logic —
progressForTransfer/Receiver, humanProgressLabel, aggregateReceiverProgress,
the refresh trigger, and the SendScreen snapshots — now compares enum cases
instead of literals. TransferProgress.phase/kind are the enums directly, so
constructions read `phase: .transfer, kind: .progress`. The two ad-hoc
phase/kind Sets collapse into "is a recognized case" (non-nil) checks.

apple/VniDrop/Core/CoreRepository.swift

@@ -298,14 +298,15 @@ private extension CoreEvent {
 	}
 }
 
-private let refreshPhases: Set<String> = ["lifecycle", "error", "ticket", "import", "download", "export", "handshake"]
-private let refreshKinds: Set<String> = [
-	"started", "done", "created", "failed", "cancelled", "share-stopped", "found-collection", "connected",
+private let refreshPhases: Set<EventPhase> = [.lifecycle, .error, .ticket, .importing, .download, .export, .handshake]
+private let refreshKinds: Set<EventKind> = [
+	.started, .done, .created, .failed, .cancelled, .shareStopped, .foundCollection, .connected,
 ]
 
 private extension CoreEventModel {
 	var shouldRefreshTransfers: Bool {
-		refreshPhases.contains(phase) && refreshKinds.contains(kind)
+		guard let eventPhase, let eventKind else { return false }
+		return refreshPhases.contains(eventPhase) && refreshKinds.contains(eventKind)
 	}
 }