chore(release): v0.4.0-alpha.1

[Shewart]

Summary

Prepares the first 0.4 prerelease.

• Release notes: a ShellUI v0.4.0-alpha.1 section covering what's new since 0.3.2:
  • 14 new components and compositional parts for 8 existing ones;
  • dashboard setup in init, restyled sample pages and terminal loaders;
  • ASP.NET Core Identity support with the auth-01/02/03 blocks;
  • the rebuilt Loading and Command;
  • the pre-alpha fixes.
    The one breaking change is Calendar's SelectedDateChanged, now EventCallback<DateTime?>. scripts/extract-release-notes.sh 0.4.0-alpha.1 extracts it for the release workflow.
• The 0.3.1 and 0.3.2 release notes, which were only on release/v0.3, are added to main.
• Docs (README, CLI installation, CLI reference, FAQ, quick start, versioning) now name 0.3.2 as the latest stable release and 0.4.0-alpha.1 as a prerelease installed with --version 0.4.0-alpha.1.
• Directory.Build.props already sets 0.4.0 + alpha.1.

Release checks

• Release build: 0 warnings; 303 tests pass.
• Every one of the 93 direct targets installed alone into a fresh .NET 10 app and built: 93 of 93 pass.
• All 93 targets installed together into an app named my-app with init --dashboard 02: builds with 0 warnings on .NET 8, 9 and 10.
• Packed CLI installed from its .nupkg: reports 0.4.0-alpha.1. A fresh Identity app with init --dashboard 02 and add auth-01 data-table chat qr-code builds with 0 warnings.
• Packed ShellUI.Components in a fresh app, checked in the browser:
  • window.ShellUI loads with no <script> tag;
  • ThemeToggle changes the theme, and Calendar @bind-SelectedDate works with DateTime?;
  • Command runs CommandItem.Action, and Popover closes on Escape;
  • MultiSeriesChart draws and Loading renders.

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