fix(csproj): re-add klear-attach.png embed entry (VS save stripped it)

Visual Studio rewrote the legacy VSTO csproj on its next save and
dropped the EmbeddedResource entry for the paperclip icon — without
it the new SaveAttachments ribbon button has no image at runtime and
the file isn't shipped in the assembly. Add it back next to the four
other Klear icons.

src/OutlookAddin/OutlookAddin.csproj

@@ -270,6 +270,9 @@
     <EmbeddedResource Include="Images\klear-compose.png">
       <LogicalName>OutlookAddin.Images.klear-compose.png</LogicalName>
     </EmbeddedResource>
+    <EmbeddedResource Include="Images\klear-attach.png">
+      <LogicalName>OutlookAddin.Images.klear-attach.png</LogicalName>
+    </EmbeddedResource>
     <Compile Include="Services\AddInHost.cs">
       <SubType>Code</SubType>
     </Compile>