Review breakdown: show each deck's own activity total

Follow-up to the smart-review breakdown: "I only have 2 decks" turned out to
be three deck cards (one clipped at the window edge) and 15 + 13 + 6 = 34
due. The line now carries each deck's activity total next to its due count -
"Due by deck: Sky deck - 15 of 15 - Humanismus - 13 of 15 - ... - 6 of 13" -
so the arithmetic is checkable inline without opening a deck.

groupByDeck returns {label, count, total}; new i18n key review.dueOfTotal
(en + cs). review-test pins the format. Version 0.6.9, SW v91.

README.md

@@ -1492,6 +1492,14 @@ Things I chose while building, with the reasoning:
     into view as you type. No strings, so no i18n; the additive change sits on top of the merged
     scene-heat rework unchanged.
 
+100. **The review breakdown carries each deck's own total.** The follow-up to 99: "bro its not
+    possible, I only have 2 decks" — the screenshot showed three deck cards (one clipped at the
+    window edge) and a breakdown of 15 + 13 + 6 = 34, so the count was right and the *number of
+    decks* was the misread. To make that checkable inline, each entry now carries the deck's
+    activity total next to its due count — "Due by deck: Renesanční… · 15 of 15 · Humanismus… ·
+    13 of 15 · Renesance… · 6 of 13" — so the arithmetic (34 due out of 43 activities) is
+    verifiable without opening a single deck. review-test pins the format.
+
 99. **The smart review names its decks.** "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 count
     itself was honest: `dueItems`/`mistakeItems` only resolve live (deck, activity) pairs, so a