feat(apple): generate type-safe L10n accessors and migrate all key literals

Replaces every stringly-typed localization key in the Apple app with
compile-time-checked accessors generated from localization/strings.json.
A mistyped key is now a build error instead of a silent fallback to the
raw key at runtime. The runtime path is unchanged: plain keys are
String.LocalizationValue constants resolved with String(localized:) and
Apple's String Catalog still does the lookup; keys with arguments become
typed, named functions applying args through String(format:).

Generator: new renderSwiftAccessors emits apple/VniDrop/Generated/L10n.swift,
wired into generate. Renamed generic arg1/arg2 tokens on four keys to
semantic names (receiver, transferName, deviceId) and updated their context
notes; positional output is unchanged so .xcstrings (bar the 4 comments)
and the Android XML regenerate identical.

Migration: every key-carrying value flipped to String.LocalizationValue
end to end, resolved only at the leaf. Zero key literals and zero
LocalizedStringKey remain in app or test code. macOS build passes; iOS
test run pending.

apple/VniDrop/Features/Approvals/ApprovalCoordinator.swift

@@ -149,12 +149,9 @@ final class ApprovalCoordinator: ObservableObject {
 		for request in pending where !publishedNotificationIds.contains(request.id) {
 			let receiver = request.receiverName
 				?? request.receiverDeviceName
-				?? String(localized: "approval_nearby_device")
-			let title = String(localized: "approval_connection_request")
-			let body = String(
-				format: String(localized: "approval_request_body"),
-				receiver, request.transferName
-			)
+				?? String(localized: L10n.Approval.nearbyDevice)
+			let title = String(localized: L10n.Approval.connectionRequest)
+			let body = L10n.Approval.requestBody(receiver: receiver, transferName: request.transferName)
 			let result = await notifications.publish(
 				LocalNotification(id: Self.notificationId(request.id), title: title, body: body)
 			)