fix: v0.3.3 – theme CSS 404, Command actions, Escape on Dropdown and Popover, SidebarProvider reloads

[Shewart]

Patch release for 0.3, porting the non-breaking fixes from #41 plus the theme CSS fix.

• Theme CSS 404 (package): shellui-theme.css no longer starts with @import "tailwindcss";, so linking it directly no longer logs a 404. The CSS build script adds the import itself; shellui-all.css is unchanged.
• Command runs CommandItem.Action (package and template): it runs the item's Action, then raises CommandSelected, like CommandPalette. Ported by hand, since 0.3's Command predates the compositional rewrite on main.
• Escape closes Dropdown and Popover (package and templates).
• SidebarProvider template: also catches JSDisconnectedException on dispose, so full reloads no longer log it twice. The demo app's copy on 0.3 already catches everything, so it is unchanged.
• Tests: PackageBehaviorTests covers the Command action and Escape on both components. The Command test clicks the item's <button>, because 0.3 has no role="option".
• chore(release): v0.3.3: version bumped in the same 11 files as 0.3.2, plus a v0.3.3 section in docs/RELEASE_NOTES.md.

Checked:

• Release build has 0 warnings and all 159 tests pass, including on the test commit by itself
• scripts/extract-release-notes.sh 0.3.3 extracts the new section
• The CSS bundle builds
• ShellUI.CLI and ShellUI.Components both pack as 0.3.3