Upgrade projects to .NET 10

[magiccodingman]

Summary

• retarget every project to net10.0 and add a .NET 10 SDK policy
• align ASP.NET Core, Blazor, UI, query, Playwright, and VSTest-compatible test dependencies
• support the C# 14 ReadOnlySpan expression shape used by array Contains queries
• migrate the standalone example from removed legacy APIs to the current repository/query API
• make browser tests deterministic with bounded concurrency, immediate input binding, and awaited IndexedDB deletion

Validation

• dotnet build Magic.IndexedDb.sln --configuration Release --no-restore (0 errors)
• dotnet build IndexDb.Example/IndexDb.Example.csproj --configuration Release --no-restore (0 warnings, 0 errors)
• dotnet test E2eTest/E2eTest.csproj --configuration Debug --no-build --no-restore --settings E2eTest/test.runsettings (96 passed)
• verified the generated NuGet package contains lib/net10.0 and the static web assets