UI: Billing & payments

Reference for the billing page, change-plan dialog, usage details, invoice detail, the top-up dialog, and post-checkout pages.

Billing page

Route: /billing. Sections on one page:

Low-balance banner and scheduled plan-change banner when applicable. The scheduled-change banner carries Cancel and Replace actions while the switch is still pending.
Summary cards — balance, plan, quota. The plan card shows a badge with the target plan and date when a switch is queued.
Change plan tiles opening the change-subscription dialog.
Usage period summary linking to usage details.
Balance history (paginated). Entries are typed — top-ups, usage, renewals, adjustments, Invoice paid, and Invoice correction when a recorded bank payment is later corrected. The ledger is append-only, so a correction is its own signed entry next to the original rather than a change to it.
Invoices table; each row links to the invoice detail. A Top up action opens the top-up dialog.

Opened from a plan tile. Alongside the target plan it asks when the switch applies — immediately, at the end of the current period, or on a date (bounded by the period end). Applying before the period ends shows how many included checks would be forfeited and requires enough balance for the new plan's full price; a queued switch has neither constraint.