TAB map content centred again; key bindings no longer pass on Ctrl/Alt

- megamap: the zoomed view (0x6cc950) is shared by the large map and the
  TAB overview map; its centre is now set per call from the drawing
  window's offset (hud::DrawOffsetX) instead of fixed to the render width
- input: drop the Ctrl/Alt pass-through; GetKeyState reports Alt as held
  after Alt+Tab, which switched all bindings back to the game's handling

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

src/mods/input.cpp

@@ -10,8 +10,10 @@
 // hotkey post that hotkey's key event to the game's event kernel, the way the window
 // procedure does (the kernel dispatches it right away, on the window thread).
 //
-// While a text field has the keyboard, or Ctrl / Alt is held, keys pass
-// through unchanged.
+// While a text field has the keyboard, keys pass through unchanged. (Keys
+// with Ctrl / Alt held used to pass too; GetKeyState reports Alt as held after
+// Alt+Tab until it is pressed again in the game, which switched the bindings
+// off. Alt+key arrives as WM_SYSKEYDOWN and is not handled here anyway.)
 //
 // sacred_re.ini (key names: A-Z, 0-9, F1-F24, Space, None):
 //   [keys]
@@ -173,10 +175,6 @@ void Release(const Binding& binding, int vk) {
     }
 }
 
-bool ModifierHeld() {
-    return (GetKeyState(VK_CONTROL) & 0x8000) != 0 || (GetKeyState(VK_MENU) & 0x8000) != 0;
-}
-
 // Virtual keys whose WM_KEYDOWN was taken: their WM_CHAR / WM_KEYUP are
 // swallowed too, even if the state changed in between.
 bool g_taken[256] = {};
@@ -212,7 +210,7 @@ bool HandleWindowMessage(HWND, UINT message, WPARAM wParam, LPARAM lParam) {
         const bool repeat = (lParam & (1 << 30)) != 0;
         if (!repeat) {
             g_taken[vk] = false;
-            if (ModifierHeld() || TypingIntoTextField()) {
+            if (TypingIntoTextField()) {
                 return false;
             }
             const Binding* binding = BindingFor(vk);