Move the app's markup to the D components and Tailwind 4

The pages and components now use the daisyUI wrappers and the neo-* utilities
instead of Bulma and the neomorph classes:
- buttons are DButton, with pressed states as Active;
- nav links are btn / btn-active;
- the filter and composer selects are DSelect with a prefix icon;
- the composer's fields are DInput and DTextarea;
- the message options and scope pickers are DDropdown, which now close on an
  outside click and on Escape;
- the settings and admin sections are DCollapse;
- the dark-mode switch is a DToggle with sun and moon icons;
- the hue slider is a DRange on the rainbow track.

DropdownButton, OpenDownContainer and LoadingData are gone. The loader is
DLoading, whose animation runs; the old one's keyframes were never defined.
Icons coloured with Bulma's has-text-* now get daisyUI's text-info, success,
warning and error, which had no rules before.

Tailwind 3 to 4 fixes:
- space-x/y become gap, which also handles the flex-col-reverse feeds;
- !rounded-lg becomes rounded-lg!;
- drop-shadow becomes drop-shadow-sm;
- text-md becomes text-base.
The thread page marks its message with Content's new Highlighted parameter
rather than a second shadow size.

neo.css: a select's prefix icon gets the room daisyUI leaves for a span.label,
and the inner select lets the well show through.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

Shared/LoginDisplay.razor

@@ -3,12 +3,12 @@
 
 <AuthorizeView>
 	<Authorized>
-		<button class="button" @onclick="BeginSignOut">
+		<DButton OnClick="BeginSignOut">
 			@Localizer["Logout"]
-		</button>
+		</DButton>
 	</Authorized>
 	<NotAuthorized>
-		<NavLink ActiveClass="neoBtnSmallInsetPlain" class="button is-rounded neoBtnSmallPlain" href="authentication/login">
+		<NavLink ActiveClass="btn-active" class="btn" href="authentication/login">
 			@Localizer["Login"]
 		</NavLink>
 	</NotAuthorized>