[feature/frontend] Add player for audio files; use thumbnail for poster (#3099)

* [feature/frontend] Audio player for audio media types

* use video preview images for previews instead of video itself

* don't preload

* update tests for new zork status

* collapse media gallery into single row when small

internal/api/model/attachment.go

@@ -90,12 +90,23 @@ type Attachment struct {
 	// A hash computed by the BlurHash algorithm, for generating colorful preview thumbnails when media has not been downloaded yet.
 	// See https://github.com/woltapp/blurhash
 	Blurhash *string `json:"blurhash"`
+}
 
-	// Additional fields not exposed via JSON
-	// (used only internally for templating etc).
+// WebAttachment is like Attachment, but with
+// additional fields not exposed via JSON;
+// used only internally for templating etc.
+//
+// swagger:ignore
+type WebAttachment struct {
+	*Attachment
 
-	// Parent status of this media is sensitive.
-	Sensitive bool `json:"-"`
+	// Parent status of this
+	// media is sensitive.
+	Sensitive bool
+
+	// MIME type of
+	// the attachment.
+	MIMEType string
 }
 
 // MediaMeta models media metadata.