Fix stale Plan tab on plan switch; replace segmented toggle with title picker

[bmingles]

Bug fix

Switching the active plan while the Plan tab stayed mounted showed stale content — the previously active plan's day/chapter breakdown kept rendering instead of the newly selected plan's.

Root cause: ChapterGroupList's <For> over group names snapshotted each group's chapters into a plain const chapters = props.data[groupName] before returning JSX. Day names ("Day 1", "Day 2", ...) are identical strings across every plan, so <For> — which is keyed by value — never re-invoked that callback on a plan switch. The snapshot froze at whichever plan was active on first render.

I confirmed the underlying activePlanId/perDayTagData signal chain was already firing correctly (instrumented planGroups's createMemo and watched it recompute on every toggle) — only the rendered output was stale. The fix keeps the props.data[groupName] lookup inline in the JSX instead of pre-computing it, so it compiles to a reactive getter rather than a frozen snapshot.

UX change

Replaced the segmented-control plan toggle (from the previous PR) with PlanPicker, an iOS "tap the title to switch context" menu — the pattern Mail and Reminders use for their inbox/list pickers. The segmented control didn't scale past a couple of plans (not enough horizontal room); this does, and it only appears once there's more than one plan to switch between.

Test plan

• npm run build passes
• tsc --noEmit passes
• Reproduced the stale-content bug in a headless browser before the fix (Day 1 kept showing the old plan's chapters — Genesis 1-3, Matthew 1-2 — after switching to a Genesis-only plan), confirmed the fix resolves it, and confirmed it round-trips cleanly switching back and forth several times
• Verified the new PlanPicker: hidden with one plan (shows plain "Plan" title), shows "{active plan name} ▾" with 2+ plans, opens a menu with a checkmark on the active plan, closes on selection or on an outside click, and correctly updates both the title and the rendered day content — tested with 5 plans to confirm it doesn't run into the segmented control's space problem

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