feat: render particle clouds for selected tags

lib/data/repositories/phoenix_tag_repository.dart

@@ -53,13 +53,21 @@ class PhoenixTagRepository implements TagRepository {
       });
 
   @override
-  Stream<List<Particle>> watchParticleCloud() =>
-      realtime.channel('localiserd').map((payload) {
-        final list = payload['particles'] as List<dynamic>? ?? [];
-        return list
-            .map((j) => Particle.fromJson(j as Map<String, dynamic>))
-            .toList();
-      });
+  Stream<ParticleSnapshot> watchParticleCloud(String tagId) =>
+      realtime
+          .channelMessages('particles:$tagId')
+          .where((m) => m.event == 'particles_updated')
+          .map((m) {
+            final est = m.payload['estimate'] as Map<String, dynamic>;
+            final list = m.payload['particles'] as List<dynamic>;
+            return ParticleSnapshot(
+              tagId: tagId,
+              estimate: Estimate.fromJson(est),
+              particles: list
+                  .map((j) => Particle.fromJson(j as Map<String, dynamic>))
+                  .toList(),
+            );
+          });
 
   @override
   Stream<Map<int, List<String>>> watchRoomOccupancy() async* {

lib/data/repositories/tag_repository.dart

@@ -11,8 +11,8 @@ abstract class TagRepository {
   /// Live stream of all tag positions, pushed by localiserd over Phoenix channel.
   Stream<List<TagPosition>> watchPositions();
 
-  /// Live stream of particle filter cloud snapshots.
-  Stream<List<Particle>> watchParticleCloud();
+  /// Live stream of particle filter cloud snapshots for [tagId].
+  Stream<ParticleSnapshot> watchParticleCloud(String tagId);
 
   /// Room occupancy delta stream.
   /// room_id -> list of tag_id strings currently in that room.