R9 Web Push in decePub: one subscription per persona, each with its own token and registration

Settings gets "Notifications on this device" (PushEditor): personas, alerts in four groups, policy, a test
notification, after a one-time notice of what the push service learns. Each persona ticked gets its own service
worker registration (push-worker.js at push/{slot}/), so its own endpoint and keys, subscribed with its own token
(IHttpService's *As); nothing PrivaPub stores ties two personas together and the worker never reads the payload's
token. PushService follows the tokens (re-subscribing after a renewal), reconciles at every session start, turns
off before sign-out and drops deleted or suspended personas. A click opens that persona's notifications; the app
badge counts the unread ones. Exchanges now ask for the push scope.

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

Models/Mastodon/WebPush.cs

@@ -0,0 +1,55 @@
+using System.Text.Json.Serialization;
+
+namespace decePubClient.Models.Mastodon;
+
+/// <summary>Mastodon's WebPushSubscription (/api/v1/push/subscription): one per access token, so one per persona.
+/// Alerts holds every alert PrivaPub knows, true or false.</summary>
+public class WebPushSubscription
+{
+	public string Id { get; set; }
+	public string Endpoint { get; set; }
+	public bool Standard { get; set; }
+	public Dictionary<string, bool> Alerts { get; set; } = [];
+	/// <summary>The server's VAPID public key, URL-safe base64.</summary>
+	public string ServerKey { get; set; }
+	/// <summary>all, followed, follower or none.</summary>
+	public string Policy { get; set; }
+}
+
+/// <summary>POST /api/v1/push/subscription as JSON: the browser's subscription and what it is pushed. PrivaPub reads it as
+/// Mastodon's flattened parameters (subscription[endpoint], subscription[keys][p256dh], data[alerts][mention], ...).</summary>
+public class PushSubscriptionForm
+{
+	public PushEndpoint Subscription { get; set; } = new();
+	public PushData Data { get; set; } = new();
+}
+
+/// <summary>The browser's push subscription: where the push service takes the pushes, and the keys they are encrypted
+/// to. Standard: RFC 8291's aes128gcm (with RFC 8292's VAPID header), which every browser that pushes decrypts.</summary>
+public class PushEndpoint
+{
+	public string Endpoint { get; set; }
+	public PushKeys Keys { get; set; } = new();
+	public bool Standard { get; set; }
+}
+
+/// <summary>The browser's P-256 public key and authentication secret, URL-safe base64.</summary>
+public class PushKeys
+{
+	[JsonPropertyName("p256dh")]
+	public string P256dh { get; set; }
+	public string Auth { get; set; }
+}
+
+/// <summary>What a subscription is pushed: each alert on or off (one left out is off), and whose.</summary>
+public class PushData
+{
+	public Dictionary<string, bool> Alerts { get; set; } = [];
+	public string Policy { get; set; }
+}
+
+/// <summary>PUT /api/v1/push/subscription: data[alerts] and data[policy] replace what the subscription had.</summary>
+public class PushDataForm
+{
+	public PushData Data { get; set; } = new();
+}