Feature: screen preview thumbnail on host double-click

Server sends COMMAND_SCREEN_PREVIEW_REQ when user double-clicks an
active (non-Locked/Inactive) host that advertises CLIENT_CAP_SCREEN_PREVIEW.
Client BitBlts primary screen, encodes to JPEG via GDI+ and replies. The
existing STATIC tooltip is replaced with a self-drawn CPreviewTipWnd
showing the thumbnail above the host info text, with wide-character
rendering so the popup also works on non-Chinese servers.

- Quality tiers reuse QualityProfile pattern: PreviewProfile + 6 levels
  driven by GetTargetQualityLevel (FRP-aware), with 4K/ultrawide auto
  upscale on Ultra/High tiers up to min(screenWidth/4, 1280).
- Client limits to 1 in-flight capture via atomic counter to defend
  against flood/DoS; Send2Server is already mutex-serialized.
- Server validates responses by reqId only (single in-flight tip);
  4s arrival timeout marks "preview unavailable" without blocking the
  text fallback path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/2015Remote/2015Remote_vs2015.vcxproj

@@ -338,6 +338,7 @@
     <ClInclude Include="FeatureLimitsDlg.h" />
     <ClInclude Include="FrpsForSubDlg.h" />
     <ClInclude Include="PluginSettingsDlg.h" />
+    <ClInclude Include="PreviewTipWnd.h" />
     <ClInclude Include="TriggerSettingsDlg.h" />
     <ClInclude Include="proxy\HPSocket.h" />
     <ClInclude Include="proxy\HPTypeDef.h" />
@@ -388,6 +389,7 @@
       <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Release|x64'">NotUsing</PrecompiledHeader>
     </ClCompile>
     <ClCompile Include="PluginSettingsDlg.cpp" />
+    <ClCompile Include="PreviewTipWnd.cpp" />
     <ClCompile Include="TriggerSettingsDlg.cpp" />
     <ClCompile Include="WebService.cpp" />
     <ClCompile Include="..\..\client\MemoryModule.c">