Add global mini-player and improve configuration

- Add global activeRoom store for persistent WebSocket connection
- Add MiniPlayer component for playback controls across pages
- Add chunked S3 streaming with 64KB chunks and Range support
- Add queue item removal button
- Move DB credentials to environment variables
- Update .env.example with DB configuration

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/services/s3.py

@@ -75,3 +75,40 @@ def get_file_content(s3_key: str) -> bytes:
     client = get_s3_client()
     response = client.get_object(Bucket=settings.s3_bucket_name, Key=s3_key)
     return response["Body"].read()
+
+
+def get_file_size(s3_key: str) -> int:
+    """Get file size from S3 without downloading"""
+    client = get_s3_client()
+    response = client.head_object(Bucket=settings.s3_bucket_name, Key=s3_key)
+    return response["ContentLength"]
+
+
+def get_file_range(s3_key: str, start: int, end: int):
+    """Get a range of bytes from S3 file"""
+    client = get_s3_client()
+    response = client.get_object(
+        Bucket=settings.s3_bucket_name,
+        Key=s3_key,
+        Range=f"bytes={start}-{end}"
+    )
+    return response["Body"].read()
+
+
+def stream_file_chunks(s3_key: str, start: int = 0, end: int = None, chunk_size: int = 64 * 1024):
+    """Stream file from S3 in chunks (default 64KB chunks)"""
+    client = get_s3_client()
+
+    if end is None:
+        range_header = f"bytes={start}-"
+    else:
+        range_header = f"bytes={start}-{end}"
+
+    response = client.get_object(
+        Bucket=settings.s3_bucket_name,
+        Key=s3_key,
+        Range=range_header
+    )
+
+    for chunk in response["Body"].iter_chunks(chunk_size=chunk_size):
+        yield chunk