CmdPal: Fix "Open Command Palette" dock item

[jiripolasek]

Summary of the Pull Request

This PR fixes the "Open Command Palette" dock item.

Dock only opens Command Palette for page commands (see DockControl.InvokeItem). The recent dock home change introduced GoHomeDockCommand as an invokable command, so the Palette no longer opened from the dock item.

• Restores dock home to use the shared root page.
• Adds a deferred root page accessor to avoid DI cycles.

PR Checklist

• Closes: CmdPal: Open Command Palette dock button is not working #49089

• Communication: I've discussed this with core contributors already. If the work hasn't been agreed, this work might be rejected
• Tests: Added/updated and all pass
• Localization: All end-user-facing strings can be localized
• Dev docs: Added/updated
• New binaries: Added on the required places
  • JSON for signing for new binaries
  • WXS for installer for new binaries and localization folder
  • YML for CI pipeline for new test projects
  • YML for signed pipeline
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[michaeljolley]

I don't think I'm understanding why this complexity is needed. When I click the cmdpal "button" on the dock, cmdpal opens and goes home. What am I missing?

[jiripolasek]

I don't think I'm understanding why this complexity is needed. When I click the cmdpal "button" on the dock, cmdpal opens and goes home. What am I missing?

DockControl.IsPageCommand returns false for GoHomeDockCommand, which prevents it from showing the Palette:

PowerToys/src/modules/cmdpal/Microsoft.CmdPal.UI/Dock/DockControl.xaml.cs

Lines 448 to 453 in de48594

	private static bool IsPageCommand(ICommand? command)
	{
	// A Page command is one that's not directly invokable - selecting it
	// navigates into a page rather than performing an action in place.
	return command is not null and not IInvokableCommand;
	}

PowerToys/src/modules/cmdpal/Microsoft.CmdPal.UI/Dock/DockControl.xaml.cs

Lines 437 to 440 in de48594

	if (IsPageCommand(command.Model.Unsafe))
	{
	WeakReferenceMessenger.Default.Send<RequestShowPaletteAtMessage>(new(pos, hwnd));
	}

We can either add an exception for this, add a new message, or revert to using the main list page as a command. IIRC, that was the original solution.

---

cd7465e removed dependency on the root page to avoid circular dependency (see commit description):

• Circular DI dependency resolved: BuiltInsCommandProvider no onger depends on IRootPageService. Previously, it required the IRootPageService solely for the dock command to open Command Palette (using the RootPage as its command.) Now, it uses a new GoHomeDockCommand which returns CommandResult.GoHome() with the existing onBeforeShowConfirmation callback to show the palette at the dock button position.

[michaeljolley]

One nit, otherwise 👍🏼