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/api.ts

@@ -110,6 +110,14 @@ export interface LibraryFilter {
   legal_in?: string | null;
   /** Only cards that can head a Commander deck. */
   can_be_commander?: boolean;
+  /** Only cards printed in this set (matched against printings.set_code).
+   *  Lets the release browser reuse the whole criteria pipeline. */
+  set_code?: string | null;
+  /** Only cards with an empty color identity — a colorless commander's pool.
+   *  Separate from the color bitmasks, where 0 means "no filter". */
+  colorless_identity?: boolean;
+  /** Only cards that are themselves colorless. */
+  colorless_colors?: boolean;
   /** Printed power/toughness. Cards printed with "*" or "1+*" are excluded,
    *  since those can't be compared numerically. */
   power_min?: number | null;