Smart review: name the source deck on every card, break the counts down

"It contains mistakes I either did more than once or from decks that I've
removed - there's no way there's 34 to repeat with 2 decks." The counts were
honest (dueItems/mistakeItems only resolve live deck+activity pairs; a seeded
repro with 37 SRS rows and 30 live shows "30 due"), but nothing in the UI said
where an item came from: a deck created twice from the same notes shows every
question twice, and a deck that survived a delete or a sync looks like a ghost.
Both read as a broken list.

- SessionFeed gains showDeck (review + mistakes): a deck chip above every
  card, so two identical questions are visibly two decks.
- The Smart review card breaks its numbers down under the buttons:
  "Due by deck: Sky deck - 17 - Sky deck (2) - 17", capped at three decks
  plus "+n more" (groupByDeck in lib/learning).
- New i18n keys (en + cs, plural forms for "+n more").

review-test pins it: a twin-deck seed renders the breakdown and both deck
chips in the feed. Version 0.6.8, SW v90.

public/sw.js

@@ -9,7 +9,7 @@
  *
  * Bumping CACHE_VERSION is how a new deploy invalidates old assets.
  */
-const CACHE_VERSION = "freezmo-v89";
+const CACHE_VERSION = "freezmo-v90";
 const SHELL_CACHE = `${CACHE_VERSION}-shell`;
 const ASSET_CACHE = `${CACHE_VERSION}-assets`;