Fix InputSimulator wParam, PeHeaderParser double-parse, and other review issues

Bug fixes:
- InputSimulator: Pass correct button state (MK_LBUTTON/MK_RBUTTON) in wParam for button-down messages instead of 0.
- PeHeaderParser: ParseOptionalHeader now reads only the optional header, not section headers (fixes double-parse waste).
- EntryPoint: Removed useless isPe32Plus branch (AddressOfEntryPoint is at offset 16 in both PE32 and PE32+).
- RemoteWindow: Handle null foreground window case in Activate to avoid calling GetWindowThreadProcessId with HWND 0.
- RemotePointer: Remove dead null-conditional operators (encoding ??) since encoding is non-nullable.

Constants added:
- SystemMethods: MkLButton (0x0001) and MkRButton (0x0002) for mouse button state flags.

Tests: 199 passing, 4 integration/interactive skipped.

WhiteMagic/Native/SystemMethods.cs

@@ -114,6 +114,10 @@ internal static partial class NativeMethods
     internal const uint WmRButtonDown = 0x0204;
     internal const uint WmRButtonUp = 0x0205;
 
+    // Mouse button state flags for WM_*BUTTONDOWN messages
+    internal const uint MkLButton = 0x0001;
+    internal const uint MkRButton = 0x0002;
+
     internal static readonly IntPtr HwndTop = IntPtr.Zero;
 
     internal const uint SwpShowWindow = 0x0040;