R9 Web Push, then the honest version: VAPID key, push subscriptions, encrypted pushes, 4.5.0 advertised

The server's VAPID key (PushKeys, made on first need, in Mongo) is the instance API's vapid.public_key and every app's
vapid_key. /api/v1/push/subscription (POST, GET, PUT, DELETE) keeps one subscription per access token, so per persona;
every notification kept (never a filtered one) is queued as a SendPush job for the subscriptions whose alert and policy
admit it, and sent through the `push` client (the safe handler, https only) encrypted as RFC 8291 aes128gcm or the
aesgcm draft with an ES256 VAPID JWT. 404/410 delete the subscription, 429/5xx/timeouts retry, other answers drop the
push. Subscriptions end with their tokens (revocation, sessions ended, suspension, deletion, a restore); backups hold
neither keys nor subscriptions. The walk of every Mastodon 4.3-4.5 client route (docs/MASTODON-API.md) added
conversations/:id/unread, domain_blocks/preview, v2 notifications clear and PUT policy, /oauth/userinfo and stubs, so both
instance APIs now say 4.5.0 (compatible; PrivaPub <release>). The pasture gets a push sink (pushsink.test) and
scenarios/push.sh in batch A.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WpVCoDeM1qUTRp4fXQdfof

PrivaPub/Infrastructure/Data/Indexes.cs

@@ -73,6 +73,9 @@ namespace PrivaPub.Infrastructure.Data
 			await Plain<PersonaNote>(token, n => n.TargetAccountId);
 			await DB.Default.Index<SuggestionDismissal>().Key(d => d.AvatarId, KeyType.Ascending).Key(d => d.AccountId, KeyType.Ascending)
 				.Option(o => o.Unique = true).CreateAsync(token);
+			// Web Push (a new collection, R9): one subscription per access token, a persona's read when it is notified
+			await Unique<PushSubscription>(s => s.TokenId, Builders<PushSubscription>.Filter.Gt(s => s.TokenId, ""), token);
+			await Plain<PushSubscription>(token, s => s.AvatarId);
 			// the staff's log, read newest first
 			await DB.Default.Index<Models.AdminAction>().Key(a => a.At, KeyType.Descending).CreateAsync(token);