feat(billing): staff switch between managed and self-serve billing

echo/docs/billing_modes.md

@@ -0,0 +1,93 @@
+# Billing modes: managed and self-serve
+
+What this feature lets you do, from the perspective of the people using it.
+
+An account can be billed in one of two ways, and dembrane staff can move it
+between them. *Managed* means dembrane sends invoices and takes payment
+out-of-band. *Self-serve* means the customer pays by card through a subscription
+they manage themselves. There is one rule that ties it all together: while a
+customer has a live card subscription, staff cannot change their tier or their
+billing mode. The customer cancels the subscription first, so it is never left
+quietly charging.
+
+There are two people in this story: dembrane *staff*, who set how an account is
+billed, and the *customer*, who sees the result on their own billing page.
+
+## The two modes
+
+- **Managed.** dembrane invoices the customer (a payment link or a sales
+  invoice). There are no automatic card charges, no dunning, and the plan never
+  auto-expires. Staff look after it. The customer keeps full access.
+- **Self-serve.** The customer subscribes and pays by card. Charges, renewals,
+  and cancellation are all in the customer's hands on their billing page.
+
+An account can be self-serve without an active subscription right now, for
+example a free account, one whose subscription was cancelled, or one staff just
+moved off managed. It is still self-serve: the customer can subscribe whenever
+they choose.
+
+## The one rule: cancel a live subscription first
+
+If an account has a live card subscription, staff cannot change its tier or
+switch its billing mode. Both are blocked with a clear message. This is
+deliberate: flipping the account while the subscription is still active would
+leave it charging the card in the background. Ask the customer to cancel it from
+their own billing page, then the change goes through.
+
+## If you are dembrane staff
+
+You manage billing mode from the admin dashboard, on an account's actions (or an
+external workspace's actions), in the **Billing mode** section. A badge shows the
+current mode: *Managed* or *Self-serve*.
+
+### Set an account to managed
+
+Use *Set to managed billing*. The account moves to invoice billing at its
+current tier, with no automatic card charges and no auto-expiry. If the account
+has a live card subscription, this is disabled with a reason: the customer
+cancels first.
+
+### Move an account to self-serve
+
+Use *Switch to self-serve billing*. You choose what happens to the plan:
+
+- **Downgrade to Free now.** The account drops to the free tier. The customer can
+  subscribe to a paid plan whenever they want.
+- **Keep the tier until a date.** The account keeps its current tier until the
+  date you pick, then reverts to Free unless the customer subscribes before then.
+  The customer is reminded before the date.
+
+Pick one. Keeping a paid tier always needs an end date, so a paid account never
+sits on self-serve with no path to payment.
+
+### Change an account's tier
+
+Change tier from the same actions. It is blocked while a live card subscription
+exists (ask the customer to cancel first); otherwise it applies right away.
+
+## If you are a customer
+
+You see your billing on your own billing page, and it reflects your real state.
+
+- **Managed by dembrane.** You see a managed-billing panel with your dembrane
+  contact. You pay by invoice, not by card, and there are no self-serve controls
+  to worry about.
+- **Subscribed (self-serve).** You see your plan as *Active*, your next invoice,
+  and controls to change your plan, update your card, or cancel.
+- **Not subscribed, but on a paid tier.** This happens after staff move you to
+  self-serve, or after you cancel. You see that there is no active subscription,
+  and a *Subscribe* button to set one up. If staff kept your tier until a date,
+  you also see when it ends. Subscribe before then to keep it.
+- **Free.** You see a plan picker to choose a paid plan whenever you are ready.
+
+You are never shown as "active" when nothing is actually set up to bill you.
+
+## At a glance
+
+| | Managed | Self-serve |
+|---|---|---|
+| Who pays how | dembrane invoices; no card | Customer subscribes and pays by card |
+| Auto-charge / expiry | Off; staff manage it | On, once subscribed |
+| Customer billing page | Managed panel + contact | Plan, or Subscribe prompt, or plan picker |
+| Set by staff with | *Set to managed billing* | *Switch to self-serve billing* (Free now, or keep tier until a date) |
+| Change tier | Anytime | Blocked while a live subscription exists (cancel first) |

echo/frontend/src/components/billing/BillingManager.tsx

@@ -98,6 +98,11 @@ interface Overview {
 	reconcile_failed_at: string | null;
 	/** Managed by dembrane (payment_mode "offline"): hide self-serve controls. */
 	is_managed: boolean;
+	/** A live Mollie subscription exists. The "Active" UI keys off this, not
+	 *  `status` (which can be "active" with no subscription). */
+	has_active_subscription: boolean;
+	/** Customer has checked out before (Mollie customer id): winding-down vs fresh. */
+	has_payment_history: boolean;
 	account_manager: AccountManager | null;
 	billing_details: BillingDetails | null;
 }
@@ -1203,6 +1208,53 @@ export function BillingManager({
 		);
 	}
 
+	// Paid tier with no live subscription (e.g. after managed->self-serve): show an
+	// honest "subscribe" prompt, not "Active". Canceled plans keep the Resume flow below.
+	if (hasPaidPlan && !isCanceling && !overview.has_active_subscription) {
+		return (
+			<Paper withBorder p="md" radius="sm">
+				<Stack gap={12}>
+					<Group gap={8}>
+						<Text size="sm" fw={500}>
+							{tierLabel(tier)}
+						</Text>
+						<Badge size="xs" variant="light" color="yellow">
+							{endDate ? (
+								<Trans>Ends {endDate}</Trans>
+							) : (
+								<Trans>No subscription</Trans>
+							)}
+						</Badge>
+					</Group>
+					<Text size="xs">
+						{endDate ? (
+							<Trans>
+								Your {tierLabel(tier)} access ends on {endDate}, then moves to
+								Free. Subscribe to keep it.
+							</Trans>
+						) : (
+							<Trans>
+								You're on {tierLabel(tier)}, but there's no active subscription.
+								Subscribe to set up billing and keep it.
+							</Trans>
+						)}
+					</Text>
+					<Button onClick={openPlan} w="fit-content">
+						<Trans>Subscribe</Trans>
+					</Button>
+				</Stack>
+				<ChangePlanModal
+					opened={planOpen}
+					onClose={closePlan}
+					currentTier={tier}
+					defaultPeriod={period}
+					submitting={submitting}
+					onConfirm={startCheckout}
+				/>
+			</Paper>
+		);
+	}
+
 	return (
 		<Paper withBorder p="md" radius="sm">
 			<Stack gap={16}>