Split Directory.Packages.props: shared versions in root, per-product in src/

Move product-local package versions out of the root Directory.Packages.props
into per-product props files under src/<Product>/. The root file now only
contains versions for packages declared by two or more top-level products,
which is the actual shared set.

Each per-product Directory.Packages.props imports the root via
GetPathOfFileAbove so that the shared versions are inherited; this is
necessary because the .NET SDK picks the closest Directory.Packages.props
in the hierarchy and does not merge multiple ones.

Per-product file contents:
- src/cli/                    Microsoft.AspNetCore.Razor.Language,
                              Microsoft.Extensions.{CommandLineUtils,Configuration,Hosting}
- src/PostIt/                 Avalonia* and CommunityToolkit.Mvvm
- src/PostIt.Tests/           Avalonia.Headless{,XUnit}
- src/Yavsc.Org/              AsciiDocSharp*, Google.Apis.Compute.v1,
                              HigginsSoft.IdentityServer8.AspNetIdentity,
                              IdentityServer8.EntityFramework.Storage,
                              IdentityServer8.Security, IdentityServer8.Storage,
                              Microsoft.AspNetCore.Antiforgery, Authentication.Google,
                              Diagnostics.EntityFrameworkCore, Mvc.NewtonsoftJson,
                              SignalR, EntityFrameworkCore.Tools, Swashbuckle,
                              System.Security.Cryptography.Pkcs, YamlDotNet
- src/Yavsc.Org.Tests/        Microsoft.AspNetCore.Hosting,
                              Extensions.Caching.Memory, Options,
                              Options.ConfigurationExtensions,
                              Selenium.WebDriver, xunit.v3.{common,extensibility.core}
- src/Yavsc.Server/           Anthropic.SDK, Google.Apis.Calendar.v3,
                              Magick.NET-Q8-AnyCPU, MailKit, MimeKit,
                              Microsoft.AspNetCore.Http.Features, StaticFiles,
                              EntityFrameworkCore.SqlServer,
                              Npgsql.EntityFrameworkCore.PostgreSQL,
                              PayPalMerchantSDK, pazof.rules, RazorEngine.NetCore
- src/Yavsc.Web/              IdentityModel.AspNetCore

No per-product file is created for Yavsc.Api, Yavsc.Blogs, Yavsc.Abstract,
or templateWeb: Api and Blogs only declare the shared JwtBearer, Abstract
and templateWeb declare no package references at all.

Also includes a minor cosmetic update to FirstUIStript.cs (Firefox -> Chrome
driver, dedent, comment header). Tests previously failing on DataProtection
keyset / SMTP were unrelated environment issues (resolved by fixing the
SMTP password locally).

src/Yavsc.Server/Directory.Packages.props

@@ -0,0 +1,20 @@
+<Project>
+  <!-- Pull in shared package versions from the repository root. -->
+  <Import Project="$([MSBuild]::GetPathOfFileAbove('Directory.Packages.props', '$(MSBuildThisFileDirectory)../'))" />
+
+  <!-- Yavsc.Server-specific versions -->
+  <ItemGroup>
+    <PackageVersion Include="Anthropic.SDK" Version="5.10.0" />
+    <PackageVersion Include="Google.Apis.Calendar.v3" Version="1.74.0.4154" />
+    <PackageVersion Include="Magick.NET-Q8-AnyCPU" Version="14.14.0" />
+    <PackageVersion Include="MailKit" Version="4.17.0" />
+    <PackageVersion Include="Microsoft.AspNetCore.Http.Features" Version="5.0.17" />
+    <PackageVersion Include="Microsoft.AspNetCore.StaticFiles" Version="2.3.11" />
+    <PackageVersion Include="Microsoft.EntityFrameworkCore.SqlServer" Version="10.0.9" />
+    <PackageVersion Include="MimeKit" Version="4.17.0" />
+    <PackageVersion Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="10.0.2" />
+    <PackageVersion Include="PayPalMerchantSDK" Version="2.16.250" />
+    <PackageVersion Include="pazof.rules" Version="1.1.3" />
+    <PackageVersion Include="RazorEngine.NetCore" Version="3.1.1" />
+  </ItemGroup>
+</Project>