Rework the mobile UIs on native components and fix layout bugs everywhere.

Android moves to Material 3 (navigation bar, app bars, list items,
bottom sheets, pager) with a real back stack. iOS hides the tab bar in
exercises so the bottom action is reachable, aligns content, and uses
system colours so themes and dark mode work. Both pick a readable
accent tint. Desktop keeps the VLSM table inside the window and gives
statistics the same header rhythm as other pages.

Co-authored-by: Cursor <cursoragent@cursor.com>

ios/Maturita/AppModel.swift

@@ -19,6 +19,18 @@ final class AppModel: ObservableObject {
         themeId = progress.themeId
         mode = progress.mode
         lang = progress.lang
+        #if DEBUG
+        // `xcrun simctl launch <udid> org.maturita.maturita -route u1e3` opens a page for screenshots.
+        if let page = UserDefaults.standard.string(forKey: "route"), let r = routeFromPage(page) {
+            openFromSearch(r.page)
+        }
+        if let theme = UserDefaults.standard.string(forKey: "theme"), let n = Int(theme), let id = ThemeId(rawValue: n) {
+            themeId = id
+        }
+        if let m = UserDefaults.standard.string(forKey: "mode") {
+            mode = m == "dark" ? .dark : .light
+        }
+        #endif
     }
 
     var palette: Palette { themePalette(themeId, mode) }