chore(release): v0.4.0-alpha.2

[Shewart]

Release notes and version references for 0.4.0-alpha.2.

In this release (already on main):

• fix: use one Tailwind CLI per machine and survive slow downloads #48: the Tailwind CLI is downloaded once per machine and run from there, so projects hold no binary; downloads survive slow connections; init carries on if the download fails; .shellui/ is git-ignored; update moves older projects onto the shared CLI
• fix: update and remove follow installed files; TimePicker value; color-scheme #46: update installs new dependencies and keeps files you changed (--force to overwrite); remove finds layouts and custom paths; the package TimePicker value fix; color-scheme for light and dark
• fix: stop shellui-theme.css requesting tailwindcss when linked directly #44: shellui-theme.css no longer 404s when linked directly
• fix: use the ShellUI logo as the NuGet package icon #43: NuGet package icon and README logo

This PR

• Directory.Build.props: suffix alpha.2
• Docs name stable 0.3.4 and prerelease 0.4.0-alpha.2 (README, VERSIONING_STRATEGY, CLI_INSTALLATION, CLI_SYNTAX, FAQ, QUICKSTART); stable-docs links point to v0.3.4
• The version fallbacks in VersionHelper and ComponentMetadata (still 0.3.0 on main) are now 0.4.0-alpha.2
• docs/RELEASE_NOTES.md: the 0.4.0-alpha.2 section, plus the 0.3.4 and 0.3.3 sections from release/v0.3; scripts/extract-release-notes.sh 0.4.0-alpha.2 extracts it

Release checks (on 9c7cfac plus this commit)

• Release build has 0 warnings, and all 334 tests pass
• A 0.3.4 project updated with the packed alpha.2 CLI: targets refreshed, the 112 MB project copy of Tailwind removed, 54 components updated, the edited AppSidebar kept, 5 new dependencies installed, builds 0/0
• A fresh Identity app, init --yes --dashboard 02 then add auth-01 data-table chat qr-code time-picker: uses the shared Tailwind CLI and builds 0/0; .shellui holds only its .gitignore
• All 93 direct targets together in my-app build 0/0 on net8.0, net9.0 and net10.0, with no project copies of the CLI
• The packed ShellUI.Components in a browser: window.ShellUI loads, TimePicker shows its value, dark mode sets color-scheme (including the native date input), Popover closes on Escape, Command runs Action then CommandSelected, no console errors

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