feat: implement watchPositions() tag position stream

lib/data/repositories/phoenix_tag_repository.dart

@@ -38,19 +38,42 @@ class PhoenixTagRepository implements TagRepository {
   Future<void> deleteTag(int id) => tagClient.deleteTag(id);
 
   @override
-  Stream<List<TagPosition>> watchPositions() =>
-      realtime.channel('tags').map((payload) {
-        final list = payload['positions'] as List<dynamic>? ?? [];
-        return list.map((j) {
-          final m = j as Map<String, dynamic>;
-          return TagPosition(
-            tagId: m['tag_id'] as String,
-            name: m['name'] as String,
-            color: m['color'] as String,
-            roomId: m['room_id'] as int?,
-          );
-        }).toList();
-      });
+  Stream<List<TagPosition>> watchPositions() async* {
+    var tagMap = await _fetchTagMap();
+
+    await for (final occupancy in watchRoomOccupancy()) {
+      // Re-fetch on every occupancy change so name/color edits and new tags
+      // are reflected without restarting the stream.
+      tagMap = await _fetchTagMap();
+
+      final positions = <TagPosition>[];
+      for (final entry in occupancy.entries) {
+        for (final tagId in entry.value) {
+          final tag = tagMap[tagId];
+          positions.add(TagPosition(
+            tagId: tagId,
+            name: tag?.name ?? tagId,
+            color: tag?.color ?? _colorForTagId(tagId),
+            roomId: entry.key,
+          ));
+        }
+      }
+      yield positions;
+    }
+  }
+
+  Future<Map<String, Tag>> _fetchTagMap() async {
+    final raw = await tagClient.getTags();
+    return {
+      for (final j in raw.cast<Map<String, dynamic>>())
+        j['tag_id'] as String: Tag.fromJson(j),
+    };
+  }
+
+  static String _colorForTagId(String tagId) {
+    final hash = tagId.codeUnits.fold(0, (h, c) => (h * 31 + c) & 0xFFFFFF);
+    return '#${hash.toRadixString(16).padLeft(6, '0')}';
+  }
 
   @override
   Stream<ParticleSnapshot> watchParticleCloud(String tagId) =>