Add multi-select and bulk actions to the Library tab

- Checkboxes on every row/tile plus a "Select all" (filtered-set-aware,
  indeterminate-aware) toggle in the toolbar.
- A bulk-action bar appears once anything's selected: add to a deck
  ("Add 1" sets each selected card to 1 copy, "Add All" sets it to
  however many you own — the latter is the one-click fix for bulk-adding
  a stack of basic lands), set location, and adjust owned quantity by a
  configurable delta. All reuse the same per-card commands the
  single-card UI already calls, so behavior stays consistent (including
  the existing grace-period undo on quantity_owned hitting 0).
- CardTile gains a `cornerLeft` slot and `selected` prop (ring highlight,
  keeps the checkbox visible without hovering) to support this in tile
  view without disturbing the existing top-right qty-stepper corner.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/components.tsx

@@ -744,15 +744,21 @@ export function ViewToggle({
 export function CardTile({
   card,
   corner,
+  cornerLeft,
   footer,
+  selected,
 }: {
   card: CardRef;
   corner?: ReactNode;
+  /** Rendered top-left, e.g. a selection checkbox (see `selected`). */
+  cornerLeft?: ReactNode;
   footer?: ReactNode;
+  /** Highlights the tile and keeps `cornerLeft` visible without hovering. */
+  selected?: boolean;
 }) {
   const { open } = useClickPreview();
   return (
-    <div className="tile">
+    <div className={`tile ${selected ? "tile-selected" : ""}`}>
       <div className="tile-img-wrap">
         {card.image_uri ? (
           <img
@@ -765,6 +771,7 @@ export function CardTile({
         ) : (
           <div className="tile-noimg">{card.name}</div>
         )}
+        {cornerLeft && <div className="tile-corner-left">{cornerLeft}</div>}
         {corner && <div className="tile-corner">{corner}</div>}
       </div>
       {footer && <div className="tile-footer">{footer}</div>}