build/ci: create intermediate dir before Sass stamp Touch; allow manual CI dispatch

- CompileSass runs before the compiler creates obj/<cfg>/net10.0, so Touch sass.stamp
  failed on clean Release publishes (MSB3371). MakeDir fixes it for all branches/pipelines.
- Add workflow_dispatch so CI can be run manually on any branch via 'gh workflow run'.

.github/workflows/ci.yml

@@ -8,6 +8,7 @@ on:
     branches: [ "master" ]
   pull_request:
     branches: [ "master" ]
+  workflow_dispatch:
 
 jobs:
   build:

Radzen.Blazor/Radzen.Blazor.csproj

@@ -70,6 +70,8 @@
 
   <Target Name="CompileSass" BeforeTargets="MoveCss" Condition="'$(TargetFramework)' == 'net10.0'"
           Inputs="@(SassFile)" Outputs="$(IntermediateOutputPath)sass.stamp">
+    <!-- The target runs before the compiler creates the intermediate dir, so the Touch below fails on a clean build. -->
+    <MakeDir Directories="$(IntermediateOutputPath)" />
     <SassCompile InputFiles="@(SassFile)" OutputStyle="compressed" />
     <Touch Files="$(IntermediateOutputPath)sass.stamp" AlwaysCreate="true" />
   </Target>