feat(print-modal): show each printer slot's colour in the filament mapping (issue #3159)

The Print / Schedule dialog's filament mapping is where the colour a slice
asked for is compared against the colour actually loaded, and only the
left-hand side of that comparison had a swatch. The slot, and every slot in
its dropdown, was text -- and the text cannot be trusted: a slot's colour name
is resolved from the Color Catalog or, failing that, from hue, so a
third-party beige is announced as "Orange". A "Color mismatch" warning then
gives no way to tell a real mismatch from two names for the same hex without
opening the printer card in another tab, which on a farm swapping twenty or
thirty non-Bambu colours between machines is a check made many times a day.

Each slot now carries its colour and its hex, and the slot whose colour is
exactly the one the slice asked for is ticked. This works for a slot bound to
an inventory spool and for one configured through Configure Slot or on the
printer itself: the second kind has no inventory row behind it, and the
printer's own tray colour is then what draws. A bound spool contributes what a
tray record cannot -- SlotSpoolIdentity gains extra_colors and effect_type, so
a two-tone or glittery spool draws as itself rather than as its base colour.

The same treatment goes to the filament-override picker used for model-based
assignment. It is the same choice on the other dispatch path, and leaving it
text-only would have made one decision read two ways.

Both controls stop being <select>s to do it, because an <option> renders text
and nothing else. SlotPicker keeps what the select gave for free -- arrow,
Home/End, Enter and Escape keys, listbox semantics, and the border colouring
that encodes match, same-type-different-colour and not-loaded -- and is
portaled with position:fixed so it is not clipped by the dialog's own scroll
container, flipping above the row when there is no room below.

frontend/src/api/client.ts

@@ -3730,6 +3730,15 @@ export interface SlotSpoolIdentity {
   subtype: string | null;
   color_name: string | null;
   rgba: string | null;
+  /** Comma-separated hex stops for a multi-colour spool, and the effect
+   *  overlay — the two things a tray record cannot carry, so a slot swatch
+   *  can be drawn the way the inventory row draws it (#3159).
+   *
+   *  Optional rather than required: the backend sends both keys on every
+   *  binding, but a frontend running against an older one gets neither, and
+   *  every reader here already falls back to a solid swatch. */
+  extra_colors?: string | null;
+  effect_type?: string | null;
 }
 
 export interface InventoryRemainResponse {