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/release.go

@@ -0,0 +1,41 @@
+package events
+
+import (
+	"context"
+	"sync"
+)
+
+// Once returns fn wrapped so it runs at most once.
+func Once(fn func()) func() {
+	if fn == nil {
+		return func() {}
+	}
+	var once sync.Once
+	return func() { once.Do(fn) }
+}
+
+// CallRelease runs Release on PostCreated or PostedToDiscord when set.
+func CallRelease(ev any) {
+	switch e := ev.(type) {
+	case PostCreated:
+		if e.Release != nil {
+			e.Release()
+		}
+	case PostedToDiscord:
+		if e.Release != nil {
+			e.Release()
+		}
+	}
+}
+
+// SubscribeRelease runs PostedToDiscord.Release on the worker.
+func SubscribeRelease(bus *Bus) {
+	if bus == nil {
+		return
+	}
+	bus.Subscribe(func(_ context.Context, ev any) {
+		if _, ok := ev.(PostedToDiscord); ok {
+			CallRelease(ev)
+		}
+	})
+}