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/App/RootView.swift

@@ -111,7 +111,7 @@ struct RootView: View {
 		#if os(macOS)
 		NavigationSplitView {
 			List(AppDestination.allCases, selection: sidebarBinding) { destination in
-				Label(LocalizedStringKey(destination.labelKey), systemImage: destination.systemImage)
+				Label(String(localized: destination.labelKey), systemImage: destination.systemImage)
 					.tag(destination)
 			}
 			.navigationSplitViewColumnWidth(min: 180, ideal: 200, max: 260)
@@ -123,7 +123,7 @@ struct RootView: View {
 			ForEach(AppDestination.allCases) { destination in
 				screen(for: destination, windowClass: windowClass)
 					.tabItem {
-						Label(LocalizedStringKey(destination.labelKey), systemImage: destination.systemImage)
+						Label(String(localized: destination.labelKey), systemImage: destination.systemImage)
 					}
 					.tag(destination)
 			}