Align Subscription Page Header and Cards

Found while visually checking Task 8266 on /org/billing/subscription at 1440px. - With the Limits card now capped at 480px, the header's Change / Contact us button sits at the page's 64rem edge, ~550px to the right of the only content. Consider giving this page a narrower measure, so the action sits above the card it acts on. - A paid plan's SubscriptionCard still spans the full 64rem above the 480px Limits card. Give both cards the same measure so they line up. Out of scope: plan model, enforcement, billing/Stripe flows. Done means: at 1440px the header action and both cards share one column edge, at 390px nothing changes, and the SubscriptionPage unit tests are green.

Already shipped by Task 8336 (commit 3160cacc4): the page and both cards share a 480px column. Verified live: at 1440px the right edges all sit at 1199, and 390px is unchanged. SubscriptionPage tests pass 35/35. No PR.