P5: remote objects are read in every shape, and videos, events, audio and links keep their own details

- ObjectShapes reads `url`, `icon` and `image` as a value, a Link or an array; Markdown `content` (PeerTube) is
  rendered; a missing `mediaType` is inferred from the extension or the attachment type (Bridgy); alt text comes from
  `name`, `summary` or their language maps; thumbnails come from attachment `icon`, object `icon[]`, `image` or a Loops
  `preview`; durations are ISO 8601 or seconds; per-attachment `sensitive` is kept; the language falls back to
  `@context` `@language` (Pleroma); titles and excerpts are plain text; hashtags normalise with NFKC like Mastodon.
- Typed details on Post: Link (Lemmy link posts, Mbin `source` URLs, Mastodon 4.7 Link attachments with an FEP-8967
  publisher preview), Video (PeerTube files with their streams, HLS playlist, poster, captions, chapters, licence,
  channel, live state, comment policy), Audio (Funkwhale), Event (Mobilizon, Gancio, Hubzilla: times, zone, floating
  time, places and addresses, online link, capacity, status), the cover image, and the author's own source text.
- Mastodon API: a card built from those details without fetching anything, an event's "when · where" line, attachment
  thumbnails and durations, and no media file offered as a preview image.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

PrivaPub/Models/Post/PostMedia.cs

@@ -16,5 +16,8 @@ namespace PrivaPub.Models.Post
 		public int? Width { get; set; }
 		public int? Height { get; set; }
 		public float[] Focus { get; set; }
+		public string RemotePreviewURL { get; set; }//the remote thumbnail (attachment icon), served through the proxy
+		public double? DurationSeconds { get; set; }
+		public bool? Sensitive { get; set; }//Misskey marks each attachment
 	}
 }