feat(prefs): ask which view to open on, and remember the answer

`view` was component state, so a reader who preferred the timeline was put
back on the list by every reload — and which view opened at all had been
decided for them twice over: the PRD said calendar, the app shipped the list.
Neither was the reader's answer.

So the first run asks, and the tabs write to `prefs` from then on. The
question ships pre-answered with the list, because a reader cannot choose
between two layouts they have not seen and that is the one that answers "what
expires next" in a look — and each option is drawn rather than described, for
the same reason. The screen says where to change it afterwards, since the tabs
are small text in a corner.

Adds `view` to the prefs key space. Additive and defaulted, so an existing
reader's stored prefs open exactly where they did before.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

docs/DATA-MODEL.md

@@ -200,7 +200,7 @@ Namespaced, versioned, and small. Nothing here ever goes to the server.
 "gacha-tracker:v1:progress"     // { [eventId]: { status?, effort?, note?, at } }
 "gacha-tracker:v1:daily"        // { [id]: { days: ["2026-08-15", ...], at } }
 "gacha-tracker:v1:ignored"      // { [eventId]: { at } }  — "stop showing me this"
-"gacha-tracker:v1:prefs"        // { region, hiddenGames[], focusGame, sort, detectDaily,
+"gacha-tracker:v1:prefs"        // { region, hiddenGames[], focusGame, sort, view, detectDaily,
                                 //   showCompleted, showIgnored, regionConfirmed, onboarded }
 "gacha-tracker:v1:completions"  // SUPERSEDED — read once to migrate, never written
 ```