Characters: 16:9 "Spielen" screen, autosave interval option

- Shared screen kit (mods/screen, docs/screens.md): a 1365x768 canvas
  centred in the render width on our own dark background, the game's
  frames and buttons; the main menu renders full width while it is shown.
- The load window (cUI_Savegame) is replaced by the Spielen screen:
  character list, hero panel, campaign x difficulty grid, save/autosave
  choice, rename/delete/reset/new character dialogs.
- Migrated characters without a shared hero load their hero's world
  first, then start the new world.
- Options, Allgemein: autosave interval (Aus/5/10/15/30 minutes).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/mods/screen.h

@@ -0,0 +1,105 @@
+#pragma once
+// 16:9 menu screens (request of 2026-10-20, docs/screens.md): a screen of our
+// own replaces a full-screen window of the game's (its render and mouse
+// handling), laid out on a 1365x768 canvas (1920x1080 in UI units), centred in
+// the render width; wider screens only get more background at the sides. The
+// look is the game's: its frames and buttons on a dark background of ours.
+//
+// A screen hooks its window's render and event methods and calls Render /
+// Handle with a body that draws / handles in canvas coordinates with the
+// helpers below.
+
+#include <cstdint>
+#include <string>
+
+#include "game/ui/text.h"
+#include "mods/hud.h"
+
+namespace mods::screen {
+
+using game::UiRect;
+
+constexpr int kWidth = hud::kCanvasWidth;
+constexpr int kHeight = hud::kCanvasHeight;
+
+// Spacing: the game's frames reach about 0x20 beyond their rects, buttons
+// about 0x21 (measured on the options window).
+constexpr int kFrameOrnament = 0x20;
+// The frames are made of pieces of 64: other sizes leave gaps (the game's
+// frames are 384x128, 384x64; screenshot 2026-10-20).
+constexpr int kFrameStep = 64;
+constexpr int kButtonOrnament = 0x21;
+constexpr int kMargin = kFrameOrnament + 16;           // canvas edge to a panel's rect
+constexpr int kPanelGap = 96;  // between two panels' rects, as the options window's columns
+constexpr int kPanelPadding = 16;                      // panel rect to its content
+
+constexpr uint16_t kFont = 1;
+constexpr uint32_t kTextColour = 0xffe6d6aa;     // as the options' texts
+constexpr uint32_t kHeadingColour = 0xfff0c060;  // as the options' headings
+constexpr uint32_t kDimColour = 0xff8c8474;
+constexpr uint32_t kRowColour = 0x40302418;
+constexpr uint32_t kRowHoverColour = 0x80403020;
+constexpr uint32_t kRowSelectedColour = 0xc0604818;
+
+// Draws the screen of `window`: the background across the whole render
+// target, then body(context) in canvas coordinates. While `window` is shown
+// the main menu thread renders the full width (widescreen::SetWideMenuScreen).
+int Render(void* window, void* device, int (*body)(void* context), void* context);
+// Runs body(context) with the event's mouse position in canvas coordinates.
+int Handle(void* event, int (*body)(void* context), void* context);
+
+void Fill(void* device, const UiRect& rect, uint32_t colour);
+// One line of text in `rect`, centred vertically (game::kTextCenter /
+// kTextRight for horizontal alignment).
+void Text(void* device, const UiRect& rect, const std::wstring& text, uint32_t colour, uint32_t flags = 0);
+
+UiRect Inset(const UiRect& rect, int by);
+
+// A panel: a dark backdrop with the game's frame around `rect` (made anew when
+// the rect changes) and an optional heading at its top.
+class Panel {
+public:
+    explicit Panel(const char* name) : name_(name) {}
+    // The content area below the heading.
+    UiRect Draw(void* device, const UiRect& rect, const std::wstring& heading = {});
+
+private:
+    const char* name_;
+    UiRect rect_ = {};
+    uint8_t* frame_ = nullptr;
+};
+
+// A button of the game's (look and sounds of `model`, a button of the
+// window), made on first use.
+class Button {
+public:
+    Button(const char* name, std::wstring caption) : name_(name), caption_(std::move(caption)) {}
+    void Draw(void* device, const uint8_t* model, const UiRect& rect);
+    // Passes the event to the button (pressed look, sound); true for a left
+    // click on it. Only for buttons drawn this frame.
+    bool Clicked(void* event);
+    void SetCaption(const std::wstring& caption);
+
+private:
+    const char* name_;
+    std::wstring caption_;
+    uint32_t captionId_ = 0;
+    uint8_t* control_ = nullptr;
+    UiRect rect_ = {};
+    unsigned drawnFrame_ = 0;
+};
+
+// Height of the model's buttons (as the window made them).
+int16_t ButtonHeight(const uint8_t* model);
+
+// Two clicks on the same thing within the system's double-click time.
+class DoubleClick {
+public:
+    bool Click(int target);
+
+private:
+    int last_ = -1;
+    unsigned long at_ = 0;
+};
+
+} // namespace mods::screen