Fix: GitHub Actions NuGet pack failure (NU5046 icon.png missing)

PROBLEM: dotnet pack failed with NU5046 for tools projects (Demo, DebugBenchmark, Viewer) trying to pack icon.png inherited from Directory.Build.props.

SOLUTION: Added IsPackable=false to all 3 tools projects. Tools/demo apps should not be published as NuGet packages.

VERIFIED: dotnet pack SharpCoreDB.CI.slnf now succeeds without NU5046 errors.

Author: MPCoreDeveloper

tools/SharpCoreDB.DebugBenchmark/SharpCoreDB.DebugBenchmark.csproj

@@ -6,6 +6,7 @@
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <LangVersion>14.0</LangVersion>
+    <IsPackable>false</IsPackable>
     <Version>1.0.5</Version>
     <PackageId>SharpCoreDB.DebugBenchmark</PackageId>
     <Authors>MPCoreDeveloper</Authors>

tools/SharpCoreDB.Demo/SharpCoreDB.Demo.csproj

@@ -7,6 +7,10 @@
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <StartupObject>SingleFileDemo</StartupObject>
+    
+    <!-- This is a demo app, not a NuGet package -->
+    <IsPackable>false</IsPackable>
+    
     <Version>1.0.5</Version>
     <PackageId>SharpCoreDB.Demo</PackageId>
     <Authors>MPCoreDeveloper</Authors>

tools/SharpCoreDB.Viewer/SharpCoreDB.Viewer.csproj

@@ -7,6 +7,10 @@
     <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
     <LangVersion>14</LangVersion>
     <ImplicitUsings>enable</ImplicitUsings>
+    
+    <!-- This is a GUI viewer tool, not a NuGet package -->
+    <IsPackable>false</IsPackable>
+    
     <Version>1.0.5</Version>
     <PackageId>SharpCoreDB.Viewer</PackageId>
     <Authors>MPCoreDeveloper</Authors>