feat(phase-16.3): light up anonId unique-listener layer

Mint a first-party localStorage anonId, thread it onto play/share beacons,
persist it via EventController, and add all-time distinct-listener counts
(site/track/release). Storage columns + indexes already existed from 16.1.

DeepDrftPublic.Client/Services/ShareTracker.cs

@@ -1,4 +1,5 @@
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using DeepDrftModels.DTOs;
 using DeepDrftModels.Enums;
 using Microsoft.AspNetCore.Components;
@@ -14,7 +15,8 @@ namespace DeepDrftPublic.Client.Services;
 /// <para>
 /// Scoped (per-session) so the debounce memory lives for the session and resets on a fresh load, matching
 /// the "feels like one act" intent: copying the same link three times in a row is one share, not three.
-/// The beacon send is fire-and-forget; no <c>anonId</c> is sent in wave 16.1.
+/// The beacon send is fire-and-forget; the current <c>anonId</c> (wave 16.3) is read synchronously from
+/// the warmed <see cref="IAnonIdProvider"/> cache and omitted when null.
 /// </para>
 /// </summary>
 public sealed class ShareTracker
@@ -23,13 +25,20 @@ public sealed class ShareTracker
     // recommendation — long enough to fold a flurry of repeat copies into one intent.
     private static readonly TimeSpan DebounceWindow = TimeSpan.FromSeconds(60);
 
+    // Omit a null anonId from the wire payload (§2.2). Cosmetic — the API tolerates null — and does not
+    // change the integer enum encoding the 16.1 contract relies on.
+    private static readonly JsonSerializerOptions BeaconJson =
+        new() { DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull };
+
     private readonly BeaconInterop _beacon;
+    private readonly IAnonIdProvider _anonId;
     private readonly string _shareUrl;
     private readonly Dictionary<string, DateTimeOffset> _lastSent = new();
 
-    public ShareTracker(BeaconInterop beacon, NavigationManager navigation)
+    public ShareTracker(BeaconInterop beacon, IAnonIdProvider anonId, NavigationManager navigation)
     {
         _beacon = beacon;
+        _anonId = anonId;
         _shareUrl = $"{navigation.BaseUri}api/event/share";
     }
 
@@ -61,7 +70,8 @@ public sealed class ShareTracker
             TargetType = targetType,
             TargetKey = targetKey,
             Channel = channel,
-        });
+            AnonId = _anonId.Current,
+        }, BeaconJson);
 
         // Fire-and-forget — a dropped share telemetry event is acceptable.
         _ = _beacon.SendAsync(_shareUrl, json);