feat(apple): tabbed macOS Settings + stats-overlay placement/toggle + Stream menu

The macOS Settings window had outgrown one scrolling pane — split it into a tabbed
preferences window (General / Display / Audio / Controllers / Advanced). Each
settings group is now a shared @ViewBuilder section, so iOS keeps its single
grouped Form and tvOS its pushed-picker layout, each defined once. No setting
moved or dropped.

New statistics-overlay controls (Settings → Display → Statistics): a show/hide
toggle (DefaultsKey.hudEnabled) and a corner picker (HUDPlacement /
DefaultsKey.hudPlacement) — the HUD moves to the chosen corner and aligns its text
to that edge.

A Scene-level "Stream" menu (StreamCommands) carries Show/Hide Statistics (⌘⇧S)
and Disconnect (⌘D). Disconnect moved off the HUD button into the menu so it
survives the overlay being hidden, wired via .focusedSceneValue. On iOS a
material-backed exit chip appears when the HUD is hidden (touch users have no
menu/⌘D); tvOS disconnect is unchanged (Siri-Remote Menu button).

Builds on macOS/iOS/tvOS; swift test green. Adversarially reviewed (8 findings
refuted, 2 minor — the iOS exit-chip contrast fix is included here).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/apple/Sources/PunktfunkClient/PunktfunkClientApp.swift

@@ -16,6 +16,11 @@ struct PunktfunkClientApp: App {
         WindowGroup("Punktfunkempfänger") {
             ContentView()
         }
+        // The Stream menu (Disconnect ⌘D, Show/Hide Statistics ⌘⇧S) — a real menu bar on
+        // macOS, hardware-keyboard shortcuts on iPad. tvOS has neither.
+        #if !os(tvOS)
+        .commands { StreamCommands() }
+        #endif
         #if os(macOS)
         Settings {
             SettingsView()