P6 done: personas can be quoted, under the owner's default of anyone, automatically

- Our public and unlisted posts state interactionPolicy.canQuote. The policy comes from the post, then the persona
  (`source[quote_policy]`: public, followers or nobody; default public as the owner chose), and is always nobody for
  followers-only posts and DMs.
- QuoteRequests are answered with Accept{result} naming a parrot-licence at /peasants/{name}/parrot-licences/{id}
  (the route name the owner chose), or with Reject. Followers-only checks that the requester really follows.
- A licence is a QuoteAuthorization naming both posts; revoking it (POST /api/v1/statuses/:id/quotes/:quoting_id/revoke)
  marks it 410, sends Delete{licence} to the quoter and the persona's followers, and revokes our own copy of the quote.
- A quote that arrives with one of our licences is accepted only if that licence is ours, unrevoked and names exactly
  that quoting post. One persona quoting another gets a licence too.
- Mastodon API: quote_approval for our posts (automatic, followers, current_user), `quote_approval_policy` when posting,
  PUT /api/v1/statuses/:id/interaction_policy, `source.quote_policy`.

Checked live: GoToSocial still accepts our posts with the policy stated, and leaves likes, replies and boosts open.

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

PrivaPub/Federation/Controllers/PeasantsController.cs

@@ -199,6 +199,33 @@ namespace PrivaPub.Federation.Controllers
 			return Activity(note);
 		}
 
+		[HttpGet, Route("{actor}/parrot-licences/{licenceId}")]
+		public async Task<IActionResult> ParrotLicence(string actor, string licenceId, CancellationToken token)
+		{
+			var author = await _localActors.FindByUserName(actor, token);
+			var licence = author == default ? default : await DB.Default.Find<QuoteLicence>().Match(l => l.ID == licenceId && l.AuthorAvatarId == author.Id).ExecuteFirstAsync(token);
+			var quoted = licence == default ? default : await _dbEntities.Posts.MatchID(licence.PostId).ExecuteFirstAsync(token);
+			if (quoted == default)
+				return NotFound();
+			var uri = Domain.Statuses.QuoteService.LicenceUri(author, licence.ID);
+			if (licence.RevokedAt.HasValue || quoted.DeletedAt.HasValue)
+				return new ContentResult
+				{
+					Content = new JsonObject { ["@context"] = ActivityPubRenderer.ActivityStreams, ["id"] = uri, ["type"] = "Tombstone", ["formerType"] = "QuoteAuthorization" }.ToJsonString(),
+					ContentType = ActivityContentType,
+					StatusCode = StatusCodes.Status410Gone
+				};
+			return Activity(new JsonObject
+			{
+				["@context"] = ActivityPubRenderer.Context(),
+				["id"] = uri,
+				["type"] = "QuoteAuthorization",
+				["attributedTo"] = author.Uri,
+				["interactingObject"] = licence.QuotingObjectURI,
+				["interactionTarget"] = quoted.ObjectURI
+			});
+		}
+
 		[HttpGet, Route("{actor}/grunts/{activityId}")]
 		public async Task<IActionResult> Grunt(string actor, string activityId, CancellationToken token)
 		{