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/routers/tracks.py

@@ -1,6 +1,6 @@
 import uuid
 from urllib.parse import quote
-from fastapi import APIRouter, Depends, HTTPException, status, UploadFile, File, Form, Request, Response
+from fastapi import APIRouter, Depends, HTTPException, status, UploadFile, File, Form, Request
 from fastapi.responses import StreamingResponse
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy import select, func
@@ -11,7 +11,7 @@ from ..models.user import User
 from ..models.track import Track
 from ..schemas.track import TrackResponse, TrackWithUrl
 from ..services.auth import get_current_user
-from ..services.s3 import upload_file, delete_file, generate_presigned_url, can_upload_file, get_file_content
+from ..services.s3 import upload_file, delete_file, generate_presigned_url, can_upload_file, get_file_size, stream_file_chunks
 from ..config import get_settings
 
 settings = get_settings()
@@ -172,9 +172,11 @@ async def stream_track(track_id: uuid.UUID, request: Request, db: AsyncSession =
     if not track:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Track not found")
 
-    # Get full file content
-    content = get_file_content(track.s3_key)
-    file_size = len(content)
+    # Get file size from S3 (without downloading)
+    file_size = get_file_size(track.s3_key)
+
+    # Encode filename for non-ASCII characters
+    encoded_filename = quote(f"{track.title}.mp3")
 
     # Parse Range header
     range_header = request.headers.get("range")
@@ -192,11 +194,8 @@ async def stream_track(track_id: uuid.UUID, request: Request, db: AsyncSession =
         end = min(end, file_size - 1)
         content_length = end - start + 1
 
-        # Encode filename for non-ASCII characters
-        encoded_filename = quote(f"{track.title}.mp3")
-
-        return Response(
-            content=content[start:end + 1],
+        return StreamingResponse(
+            stream_file_chunks(track.s3_key, start, end),
             status_code=206,
             media_type="audio/mpeg",
             headers={
@@ -207,12 +206,9 @@ async def stream_track(track_id: uuid.UUID, request: Request, db: AsyncSession =
             }
         )
 
-    # Encode filename for non-ASCII characters
-    encoded_filename = quote(f"{track.title}.mp3")
-
-    # No range - return full file
-    return Response(
-        content=content,
+    # No range - stream full file
+    return StreamingResponse(
+        stream_file_chunks(track.s3_key),
         media_type="audio/mpeg",
         headers={
             "Accept-Ranges": "bytes",