Set the navigation and tab bars in the library's type

The screen titles were still system bold sans — `navigationTitle` renders
through UIKit, which no SwiftUI font modifier reaches, so paperSurface()
could tint the bar but never restyle its text. PaperAppearance configures
UINavigationBarAppearance once at launch: serif large and inline titles in
ink, and monospaced tab bar labels.

One trap worth recording: configuring that appearance with
configureWithOpaqueBackground() makes iOS 26 stop laying out the large
title entirely — it vanishes rather than restyling, and it does so even
with the font attributes removed, so it reads like a font problem when it
isn't. Transparent works, and is right here anyway: every screen already
paints the paper ground itself.

Verified in both schemes. Suite passes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JgLHztZGaEHvS3KNeGQmRM

Marks/MarksApp.swift

@@ -12,6 +12,8 @@ private let defaultConfig = ServerConfig(
 struct MarksApp: App {
     @State private var serverConfig: ServerConfig = ServerConfig.load() ?? defaultConfig
 
+    init() { PaperAppearance.apply() }
+
     var body: some Scene {
         WindowGroup {
             MainContainer(config: serverConfig) {