P6: quote posts, received and sent (FEP-044f and the older keys)

- Received quotes: read from `quote`, `quoteUrl`, `quoteUri`, `_misskey_quote` or a FEP-e232 Link tag; the quoted post
  is fetched once; a quoteAuthorization stamp is verified field by field on the quoted author's origin; a consent
  quote without a stamp is pending; an older-key quote of a public post is shown; Delete of a stamp revokes. Counts
  and a `quote` notification follow the accepted state. The `quote-inline` fallback survives sanitising and is removed
  from content when the real quote is shown.
- Personas quote through `quoted_status_id`: posts that state a quote policy get a QuoteRequest and stay pending until
  an Accept brings a stamp we can verify, then an Update adds quoteAuthorization; posts that state none are quoted
  the older way, without `quote`; another persona's posts cannot be quoted yet (we issue no stamps). Quoting posts
  are delivered to the quoted author too.
- Mastodon API: Status.quote (with the quoted status one level deep), quotes_count, quote_approval from the remote
  policy, GET /api/v1/statuses/:id/quotes, `quote` notifications, and api_versions.mastodon = 7.

Checked live: GoToSocial's author-only quote policy is respected.

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

PrivaPub/Federation/Objects/ObjectShapes.cs

@@ -18,6 +18,7 @@ namespace PrivaPub.Federation.Objects
 		const int CoverMaxWidth = 1280;
 		const int MaxEmojis = 64;
 		const int MaxPollOptions = 20;
+		const int MaxAudience = 32;
 
 		static readonly Dictionary<string, string> MediaTypesByExtension = new(StringComparer.OrdinalIgnoreCase)
 		{
@@ -97,6 +98,23 @@ namespace PrivaPub.Federation.Objects
 				.Take(MaxEmojis)
 				.ToList();
 
+		public static InteractionRule QuotePolicy(JsonObject note)
+		{
+			if (note["interactionPolicy"] is not JsonObject policy || policy["canQuote"] is not JsonObject canQuote)
+				return default;
+			static List<string> Who(JsonNode node) => node switch
+			{
+				JsonArray array => array.Select(Id).Where(id => id != default).Take(MaxAudience).ToList(),
+				JsonNode single when Id(single) is { } id => new List<string> { id },
+				_ => new List<string>()
+			};
+			return new InteractionRule
+			{
+				Automatic = Who(canQuote["automaticApproval"] ?? canQuote["always"]),
+				Manual = Who(canQuote["manualApproval"] ?? canQuote["approvalRequired"])
+			};
+		}
+
 		public static PostPoll Poll(JsonObject note)
 		{
 			if (Value(note, "type") != "Question")