fix(events): stop subtracting sold from amount_tickets

`amount_tickets` IS the remaining count — the backend decrements it on
every sale and increments `sold`, so the two describe the same tickets.
MyEventsPage subtracted one from the other, removing each sale twice.

Because remaining + sold is the original capacity, `amount_tickets <=
sold` first becomes true at exactly the halfway point. So the purchase
button disabled itself once an event had sold half its seats, and
"Tickets Available" under-reported all the way there.

The backend half of this shipped as aiolabs/events#59 in v1.6.1-aio.17,
which makes the mismatch worse rather than better: the server now sells
correctly while the webapp refuses to let anyone buy. On aio-demo three
events are past the threshold — "Tech Meetup" has 9 tickets left, shows
-2, and the button is dead. The API confirms they are sellable.

Also makes ticket capacity a required field, at least 1. A capacity of 0
used to mean "unlimited", but nothing on the backend agreed: both
api_get_event and api_ticket_create read `amount_tickets < 1` as sold
out, so a 0 produced an event that advertised unlimited tickets on the
card and returned 410 to every purchase. aiolabs/events#62 stops
publishing that lie; this stops the form creating it.

The payload check moves from falsy to `!== undefined`, which is what
unblocks the backend making the field required — a falsy check dropped
0 from the request entirely, so a server-side `ge=1` would have 422'd
this dialog for precisely the case users were picking.

Editing an existing zero-capacity event now opens with the field empty
rather than prefilled with 0, so the organiser has to choose.

Closes #173

src/modules/events/components/CreateEventDialog.vue

@@ -146,7 +146,11 @@ const formSchema = toTypedSchema(
         .array(z.enum(['lightning', 'fiat']))
         .min(1, 'Enable at least one payment method'),
       fiat_currency: z.string().default("USD"),
-      amount_tickets: z.number().min(0).max(100000).default(0),
+      // Required, and at least 1. A capacity of 0 used to mean
+      // "unlimited", but the backend reads `amount_tickets < 1` as sold
+      // out everywhere (aiolabs/events#34), so a 0 produced an event that
+      // advertised unlimited tickets and refused every purchase.
+      amount_tickets: z.number().min(1, 'Set how many tickets are on sale').max(100000),
       price_per_ticket: z.number().min(0).default(0),
       email_notifications: z.boolean().default(false),
       nostr_notifications: z.boolean().default(false),
@@ -195,7 +199,7 @@ const form = useForm({
     currency: 'sat',
     payment_methods: ['lightning'],
     fiat_currency: 'USD',
-    amount_tickets: 0,
+    amount_tickets: undefined,
     price_per_ticket: 0,
     email_notifications: false,
     nostr_notifications: false,
@@ -306,7 +310,9 @@ async function populateFromEvent(event: TicketedEvent) {
     currency: event.currency ?? 'sat',
     payment_methods: paymentMethodsOf(event),
     fiat_currency: event.fiat_currency ?? 'USD',
-    amount_tickets: event.amount_tickets ?? 0,
+    // 0 is no longer a valid capacity, so an existing zero-capacity event
+    // opens with the field empty and the organiser has to set a real one.
+    amount_tickets: event.amount_tickets || undefined,
     price_per_ticket: event.price_per_ticket ?? 0,
     email_notifications: event.extra?.email_notifications ?? false,
     nostr_notifications: event.extra?.nostr_notifications ?? false,
@@ -429,7 +435,8 @@ const onSubmit = form.handleSubmit(async (formValues) => {
     if (acceptsFiat && formValues.fiat_currency) {
       eventData.fiat_currency = formValues.fiat_currency
     }
-    if (formValues.amount_tickets) eventData.amount_tickets = formValues.amount_tickets
+    if (formValues.amount_tickets !== undefined)
+      eventData.amount_tickets = formValues.amount_tickets
     if (formValues.price_per_ticket) eventData.price_per_ticket = formValues.price_per_ticket
     if (selectedCategories.value.length > 0) eventData.categories = selectedCategories.value
 
@@ -693,9 +700,9 @@ const handleOpenChange = (open: boolean) => {
                 <FormItem class="min-w-0">
                   <FormLabel>Tickets</FormLabel>
                   <FormControl>
-                    <Input type="number" min="0" max="100000" placeholder="0" v-bind="componentField" />
+                    <Input type="number" min="1" max="100000" placeholder="50" v-bind="componentField" />
                   </FormControl>
-                  <FormDescription class="text-xs">0 = unlimited</FormDescription>
+                  <FormDescription class="text-xs">Total on sale</FormDescription>
                   <FormMessage />
                 </FormItem>
               </FormField>

src/modules/events/views/MyEventsPage.vue

@@ -173,7 +173,7 @@ function handleEventChanged() {
                   </div>
                   <div class="flex justify-between">
                     <span class="text-muted-foreground">Tickets Available:</span>
-                    <span class="text-foreground">{{ event.amount_tickets - event.sold }}</span>
+                    <span class="text-foreground">{{ event.amount_tickets }}</span>
                   </div>
                   <div class="flex justify-between">
                     <span class="text-muted-foreground">Price:</span>
@@ -187,7 +187,7 @@ function handleEventChanged() {
                   variant="default"
                   :disabled="
                     event.status !== 'approved' ||
-                    event.amount_tickets <= event.sold ||
+                    event.amount_tickets < 1 ||
                     !isAuthenticated
                   "
                   @click="handlePurchaseClick(event)"