Polish parent settings and subscription screens

[tpaulshippy]

Summary

Polish for the parent settings and subscription screens (light + dark themes):

• Settings — Delete Account: now a destructive red row (icon + label, #FF3B30 light / #FF453A dark) so it no longer looks identical to normal navigation rows. It keeps its chevron since it navigates to a confirmation screen; onPress unchanged.
• Settings — Log Out: restyled as an action row — tint-colored icon and label, no chevron — instead of looking like a navigation row. handleLogout unchanged.
• Settings — token usage bar: the react-native-progress bar previously rendered as an empty outlined rectangle that looked like a stray text input at 0%. It now has a visible muted track (unfilledColor/borderColor, rounded) with the tint fill proportional to usage; at 0% it clearly reads as a progress bar. The "N% of available tokens used today" label is kept.
• Subscription: "Current Plan" / "Subscribe" / "Unsubscribe" / "Restore Purchases" buttons now have white, centered, semi-bold text on the cyan/tint fill (previously dark, left-aligned, low contrast). Handlers, RevenueCat logic, alerts, and navigation are all unchanged.

Only front/app/parent/settings.tsx and front/app/parent/subscription.tsx were touched — ThemedButton and MenuItem needed no changes.

Note: app/__tests__/_layout-test.tsx fails on a clean checkout as well (pre-existing standard-navigation ESM transform issue in Jest, unrelated to this change); all 28 tests pass.

Before / After

Settings (light)

Settings (dark)

Subscription (light)

Subscription (dark)

Screenshots committed to this branch under docs/screenshots/ for review; drop them before merging if undesired.