changelog: add 1.0.8-rc15 entry

Cover the 60 commits since 1.0.8-rc14: blog attachments + Markdown
preview, the Estimate pipeline (list/edition/validation + API + EF
migrations), provider ongoing requests, file-ACL and genericEstimate
migrations, POSTIT_SETTINGS_JSON, billing filtered by user, shared
YavscMessageSender, Gitleaks CI, and the test stabilization wave.

Co-Authored-By: Claude <noreply@anthropic.com>

src/Yavsc.Org.Tests/Yavsc.Org.Tests.csproj

@@ -11,8 +11,8 @@
     <RunSettingsFilePath>$(MSBuildProjectDirectory)\test.runsettings</RunSettingsFilePath>
     <AssemblyVersion>1.1.0.0</AssemblyVersion>
     <FileVersion>1.1.0.0</FileVersion>
-    <InformationalVersion>1.1.0-beta.1+183.Branch.release-1.0.8-rc8.Sha.6cff3db32ecf72c0d2d430b7002fa7816a34e070</InformationalVersion>
-    <Version>1.1.0-beta.1</Version>
+    <InformationalVersion>1.1.0-feat-sign-estimate.1+306.Branch.feat-sign-estimate.Sha.e9a33695b38154859729b61d1280e596f1597acf</InformationalVersion>
+    <Version>1.1.0-feat-sign-estimate.1</Version>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="coverlet.collector" />
@@ -53,9 +53,9 @@
     <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" />
   </ItemGroup>
   <ItemGroup>
-      <Content Update="xunit.runner.json">
-          <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-      </Content>
+    <Content Update="xunit.runner.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
   </ItemGroup>
   <!--
     MapStaticAssets() in the production pipeline resolves
@@ -89,4 +89,4 @@
     </ItemGroup>
     <Copy SourceFiles="@(_YavscOrgStaticAssetsFiles)" DestinationFolder="$(OutDir)" />
   </Target>
-</Project>
+</Project>