fix: progress broadcasts now use correct WebSocket room names

- Fixed room name mismatch: ProgressService was broadcasting to
  'download_progress' but JS clients join 'downloads' room
- Added _get_room_for_progress_type() mapping function
- Updated all progress methods to use correct room names
- Added 13 new tests for room name mapping and broadcast verification
- Updated existing tests to expect correct room names
- Fixed JS clients to join valid rooms (downloads, queue, scan)

src/server/services/progress_service.py

@@ -133,6 +133,30 @@ class ProgressServiceError(Exception):
     """Service-level exception for progress operations."""
 
 
+# Mapping from ProgressType to WebSocket room names
+# This ensures compatibility with the valid rooms defined in the WebSocket API:
+# "downloads", "queue", "scan", "system", "errors"
+_PROGRESS_TYPE_TO_ROOM: Dict[ProgressType, str] = {
+    ProgressType.DOWNLOAD: "downloads",
+    ProgressType.SCAN: "scan",
+    ProgressType.QUEUE: "queue",
+    ProgressType.SYSTEM: "system",
+    ProgressType.ERROR: "errors",
+}
+
+
+def _get_room_for_progress_type(progress_type: ProgressType) -> str:
+    """Get the WebSocket room name for a progress type.
+    
+    Args:
+        progress_type: The type of progress update
+        
+    Returns:
+        The WebSocket room name to broadcast to
+    """
+    return _PROGRESS_TYPE_TO_ROOM.get(progress_type, "system")
+
+
 class ProgressService:
     """Manages real-time progress updates and broadcasting.
 
@@ -293,7 +317,7 @@ class ProgressService:
             )
 
         # Emit event to subscribers
-        room = f"{progress_type.value}_progress"
+        room = _get_room_for_progress_type(progress_type)
         event = ProgressEvent(
             event_type=f"{progress_type.value}_progress",
             progress_id=progress_id,
@@ -370,7 +394,7 @@ class ProgressService:
             should_broadcast = force_broadcast or percent_change >= 1.0
 
         if should_broadcast:
-            room = f"{update.type.value}_progress"
+            room = _get_room_for_progress_type(update.type)
             event = ProgressEvent(
                 event_type=f"{update.type.value}_progress",
                 progress_id=progress_id,
@@ -427,7 +451,7 @@ class ProgressService:
             )
 
         # Emit completion event
-        room = f"{update.type.value}_progress"
+        room = _get_room_for_progress_type(update.type)
         event = ProgressEvent(
             event_type=f"{update.type.value}_progress",
             progress_id=progress_id,
@@ -483,7 +507,7 @@ class ProgressService:
             )
 
         # Emit failure event
-        room = f"{update.type.value}_progress"
+        room = _get_room_for_progress_type(update.type)
         event = ProgressEvent(
             event_type=f"{update.type.value}_progress",
             progress_id=progress_id,
@@ -533,7 +557,7 @@ class ProgressService:
             )
 
         # Emit cancellation event
-        room = f"{update.type.value}_progress"
+        room = _get_room_for_progress_type(update.type)
         event = ProgressEvent(
             event_type=f"{update.type.value}_progress",
             progress_id=progress_id,