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/views/LibraryBrowser.tsx

@@ -49,6 +49,9 @@ export function LibraryBrowser({
   const [text, setText] = useState("");
   const [commander, setCommander] = useState(0);
   const [colorsInclude, setColorsInclude] = useState(0);
+  // Colourlessness can't ride in the bitmask — 0 there means "no filter".
+  const [colorlessIdentity, setColorlessIdentity] = useState(false);
+  const [colorlessColors, setColorlessColors] = useState(false);
   const [cmcMin, setCmcMin] = useState("");
   const [cmcMax, setCmcMax] = useState("");
   const [types, setTypes] = useState<string[]>([]);
@@ -119,6 +122,8 @@ export function LibraryBrowser({
       text: text.trim() || null,
       commander_identity: commander || null,
       colors_include: colorsInclude || null,
+      colorless_identity: colorlessIdentity,
+      colorless_colors: colorlessColors,
       cmc_min: cmcMin === "" ? null : Number(cmcMin),
       cmc_max: cmcMax === "" ? null : Number(cmcMax),
       types,
@@ -137,6 +142,8 @@ export function LibraryBrowser({
     text,
     commander,
     colorsInclude,
+    colorlessIdentity,
+    colorlessColors,
     cmcMin,
     cmcMax,
     types,
@@ -538,11 +545,23 @@ export function LibraryBrowser({
         <div className={`filters-more ${filtersExpanded ? "expanded" : ""}`}>
         <div className="field">
           <label>Playable in commander (color identity ⊆)</label>
-          <ColorToggles value={commander} onChange={setCommander} />
+          <ColorToggles
+            value={commander}
+            onChange={setCommander}
+            colorless={colorlessIdentity}
+            onColorlessChange={setColorlessIdentity}
+            colorlessTitle="Colorless commander — only cards with no color identity"
+          />
         </div>
         <div className="field">
           <label>Includes colors</label>
-          <ColorToggles value={colorsInclude} onChange={setColorsInclude} />
+          <ColorToggles
+            value={colorsInclude}
+            onChange={setColorsInclude}
+            colorless={colorlessColors}
+            onColorlessChange={setColorlessColors}
+            colorlessTitle="Colorless cards only"
+          />
         </div>
         <div className="field">
           <label>Mana value</label>