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>

frontend/src/stores/player.js

@@ -47,6 +47,14 @@ export const usePlayerStore = defineStore('player', () => {
     isPlaying.value = false
   }
 
+  function reset() {
+    isPlaying.value = false
+    currentTrack.value = null
+    currentTrackUrl.value = null
+    position.value = 0
+    duration.value = 0
+  }
+
   // Load saved volume
   const savedVolume = localStorage.getItem('volume')
   if (savedVolume) {
@@ -67,5 +75,6 @@ export const usePlayerStore = defineStore('player', () => {
     setVolume,
     play,
     pause,
+    reset,
   }
 })