Add colorless filters, and make set listings filterable

Colorless

There was no way to ask for colorless cards — the colour toggles are a 5-bit
WUBRG mask where 0 already means "don't filter by colour", leaving nothing to
express "no colours at all". That's exactly what you need to find a colorless
commander's card pool.

Adds a "C" pip to both colour rows, matching how ColorPips already renders
colorless cards, backed by two explicit booleans rather than a sixth bit — a
filter mask and a card's real colour mask staying the same shape is worth
keeping. The two rows mean different things and both are useful: on the
commander row C filters colour *identity*, which is the Commander rule; on the
includes row it filters the card's own colours. A card printed colorless can
still carry a coloured identity through mana symbols in its text, and it's the
identity that bars it from a colorless commander's deck.

Set listings

News > Releases had its own card path and so couldn't be filtered. A new
set_code filter (matched against printings.set_code, already ingested) lets the
set browser run through search_reference instead, so every criterion works
there identically rather than being reimplemented over a live Scryfall
response.

That alone would have cost the ability to browse an upcoming set, since
search_reference only knows downloaded card data — and upcoming sets are half
the point of the tab. So the browser picks a source per set: downloaded data
where it exists, with the full filter panel; otherwise Scryfall directly, with
the panel hidden and a line explaining why. A panel that silently does nothing
would be worse than no panel.

The source is decided by an *unfiltered* probe. Keying off whether the current
criteria match anything would flip a properly indexed set to "live" the moment
a filter excluded everything, dropping the panel exactly when it was in use.

src/components.tsx

@@ -1376,9 +1376,20 @@ export function CardTile({
 export function ColorToggles({
   value,
   onChange,
+  colorless,
+  onColorlessChange,
+  colorlessTitle,
 }: {
   value: number;
   onChange: (mask: number) => void;
+  /** Renders a "C" pip alongside the colours when provided.
+   *
+   *  Colourlessness can't live in the bitmask: 0 there already means "don't
+   *  filter by colour", so there'd be no way to say "no colours at all" — which
+   *  is exactly what you need to find a colourless commander's card pool. */
+  colorless?: boolean;
+  onColorlessChange?: (v: boolean) => void;
+  colorlessTitle?: string;
 }) {
   return (
     <span className="color-toggles">
@@ -1392,6 +1403,15 @@ export function ColorToggles({
           {c.code}
         </span>
       ))}
+      {onColorlessChange && (
+        <span
+          title={colorlessTitle ?? "Colorless"}
+          className={`pip C ${colorless ? "on" : ""}`}
+          onClick={() => onColorlessChange(!colorless)}
+        >
+          C
+        </span>
+      )}
     </span>
   );
 }