Add video picker and Discord video attachments.

The picker accepts one MP4 or WebM, the thread lightbox zooms photos, and Discord gets the video as a file on a follow-up message so photo embeds still render.

internal/events/bus_test.go

@@ -102,3 +102,44 @@ func TestBusDropsWhenFull(t *testing.T) {
 	default:
 	}
 }
+
+func TestNopReleasesPostCreated(t *testing.T) {
+	t.Parallel()
+
+	released := false
+	Nop{}.Publish(context.Background(), PostCreated{Release: func() { released = true }})
+	if !released {
+		t.Fatal("Nop.Publish did not release held upload")
+	}
+}
+
+func TestBusDropReleasesPostCreated(t *testing.T) {
+	t.Parallel()
+
+	bus := newBus(1, false)
+	bus.Publish(context.Background(), "kept")
+	released := false
+	bus.Publish(context.Background(), PostCreated{Release: func() { released = true }})
+	if !released {
+		t.Fatal("dropped PostCreated did not release held upload")
+	}
+}
+
+func TestSubscribeReleasePostedToDiscord(t *testing.T) {
+	t.Parallel()
+
+	bus := New()
+	defer bus.Close()
+	SubscribeRelease(bus)
+
+	released := make(chan struct{})
+	bus.Publish(context.Background(), PostedToDiscord{
+		PostID:  "post-1",
+		Release: func() { close(released) },
+	})
+	select {
+	case <-released:
+	case <-time.After(time.Second):
+		t.Fatal("PostedToDiscord did not release")
+	}
+}