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/UI/Components/AdaptiveDrawer.swift

@@ -41,7 +41,7 @@ private struct SheetChrome<Content: View>: View {
 			ScrollView { content().padding(.top, 4) }
 				.toolbar {
 					ToolbarItem(placement: .cancellationAction) {
-						Button(String(localized: "button_close"), action: onClose)
+						Button(String(localized: L10n.Button.close), action: onClose)
 					}
 				}
 				#if os(iOS)