events v1.6.1-aio.18 — zero capacity is sold out, not unlimited

Adds the entry alongside aio.17; older versions stay resolvable.

aiolabs/events#62: tickets_available is always published, including
zero. Omitting it meant "unlimited", but api_get_event and
api_ticket_create both read `amount_tickets < 1` as sold out — so a
zero-capacity event advertised unlimited tickets on the card while both
the detail page and the purchase returned 410. Three were live on
aio-demo.

extensions.json

@@ -345,6 +345,16 @@
             "archive": "https://git.atitlan.io/aiolabs/events/archive/v1.6.1-aio.17.zip",
             "hash": "81eb7fd85a382f72f550917951b51ed88a7ea134eb0a7fd47476128e42f1277e"
         },
+        {
+            "id": "events",
+            "repo": "https://git.atitlan.io/aiolabs/events",
+            "name": "AIO Events",
+            "version": "1.6.1-aio.18",
+            "short_description": "Zero-capacity events now read as sold out instead of advertising unlimited tickets. Omitting tickets_available meant unlimited, but every other reader treated a capacity below 1 as sold out, so those events showed a buy prompt and refused every purchase.",
+            "icon": "https://git.atitlan.io/aiolabs/events/raw/branch/main/static/image/events.png",
+            "archive": "https://git.atitlan.io/aiolabs/events/archive/v1.6.1-aio.18.zip",
+            "hash": "b33c00d4fc5ff4fd635b35e4416df991f18621615dd563bd739c1845904f2f38"
+        },
         {
             "id": "nostrclient",
             "repo": "https://git.atitlan.io/aiolabs/nostrclient",