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

Styles/neo.css

@@ -145,6 +145,18 @@
 	&:not(:where(.select-ghost, .select-neutral, .select-primary, .select-secondary, .select-accent, .select-info, .select-success, .select-warning, .select-error, .validator:user-invalid, [aria-invalid="true"])) {
 		border-color: transparent;
 	}
+
+	/* label.select: the inner select inherits the label's background and pulls itself .75rem to the left, which
+	   daisyUI expects a span.label to absorb. Let the well show through and give any other prefix (an icon) the same
+	   room. */
+	& > select {
+		background-color: transparent;
+	}
+
+	& > :first-child:not(select, .label) {
+		flex-shrink: 0;
+		margin-inline-end: .75rem;
+	}
 }
 
 @utility textarea {