Bigger decks: pick up to 30 activities, built in batches

The create wizard stopped at 15 activities because the API, the prompt and
the salvage path all capped at 18: one reply must be one valid JSON object,
and past ~18 activities models truncate or drop cards. Raising the cap alone
would have shipped decks that came back short.

- The count picker offers 8 / 10 / 12 / 15 / 20 / 30; a deck's "add more" row
  gained +15. The help line says bigger decks take longer.
- /api/generate accepts up to 30 (FREEZMO_DEFAULT_ACTIVITY_COUNT now clamps
  to 30 as well) and sizes its overall deadline from the number of model
  calls instead of a fixed two.
- generateActivities splits anything above 18 evenly across calls (30 → 15 +
  15, 25 → 13 + 12) and merges them into one deck. The first call keeps the
  "add to this deck" contract; later calls are told the title, the types
  already used and the topics already covered. A normalised content signature
  drops a card that repeats an earlier one, so the same idea never ships
  twice. requested/generated still travel in the stream meta.
- phase1-test: a stub Ollama answers two 15-card batches (the second repeats
  one card on purpose) → two calls, the even split, the "already covered"
  prompt, 29 merged cards, the duplicate shipped once, title from the first
  reply, and count 31 answered 400 (59 checks).
- wizard-test: the picker offers 30, the wizard sends count: 30, and the
  30-card deck is stored and opened (99 checks).

Version 0.8.4, SW v106.

components/UploadScreen.tsx

@@ -83,7 +83,9 @@ const DIFFICULTIES: Array<{ value: Difficulty; labelKey: string; icon: React.Rea
   { value: "hard", labelKey: "upload.hard", icon: <IceCubeIcon className="size-5" />, blurbKey: "upload.hardBlurb" },
 ];
 
-const COUNT_OPTIONS = [8, 10, 12, 15];
+/** Deck sizes the wizard offers. Above 18 the server builds the deck in
+ *  several model calls; 30 is the largest it accepts. */
+const COUNT_OPTIONS = [8, 10, 12, 15, 20, 30];
 
 const GENERATION_TIPS = ["upload.tip1", "upload.tip2", "upload.tip3", "upload.tip4"];