feat: integrate K.G.One music generation panel

- ConfigManager: add `general.kgone` config block (enabled toggle +
base URL); add `setKGOneManagedByServer()` / `isKGOneServerManaged()`
for managed deployments that supply a `kgone-server.txt` override
- App.tsx: probe for `kgone-server.txt` on startup (Content-Type guard
to avoid Vite SPA fallback false-positive)
- GeneralSettings: new K.G.One section with enable toggle + base URL
input; fields disabled when server-managed
- Toolbar: magic wand button (FaWandMagicSparkles) that toggles the
panel; disabled with reduced opacity when K.G.One is turned off;
mutually exclusive with the Chat panel
- projectStore: add `showKGOnePanel` state + `toggleKGOnePanel` action
- KGOnePanel (new): three-tab panel (Clip / Full Song / Separator)
- Clip: prompt + advanced params → POST /v1/clip/generate → poll
    /v1/clip/result → download WAV → AudioPlayer preview
- Full Song: caption + lyrics + advanced params → POST
    /v1/fullsong/generate → poll /v1/fullsong/result (live progress %
    from nested JSON string) → download MP3 → AudioPlayer preview
- Separator: reads selected audio region from OPFS via
    KGAudioFileStorage → POST /v1/separator/separate (multipart) →
    poll /v1/separator/result → parallel-download all stem files →
    multiple labeled AudioPlayer instances rendered vertically
- Shared: custom AudioPlayer (play/pause, clickable seek bar),
    spinner + hint text, error card, AbortController cleanup,
    DEBUG_MODE.KGONE-gated REQ/RES console logging

src/stores/projectStore.ts

@@ -76,6 +76,9 @@ interface ProjectState {
   // ChatBox state
   showChatBox: boolean;
 
+  // K.G.One panel state
+  showKGOnePanel: boolean;
+
   // Instrument selection panel state
   showInstrumentSelection: boolean;
   // instrumentSelectionTrackId removed; panel now follows selectedTrackId
@@ -137,6 +140,9 @@ interface ProjectState {
   setShowChatBox: (show: boolean) => void;
   toggleChatBox: () => void;
 
+  // K.G.One panel actions
+  toggleKGOnePanel: () => void;
+
   // Instrument selection panel actions
   openInstrumentSelectionForTrack: () => void;
   toggleInstrumentSelectionForTrack: () => void;
@@ -278,6 +284,9 @@ export const useProjectStore = create<ProjectState>((set, get) => {
     // Initial ChatBox state
     showChatBox: initialChatBoxState,
 
+    // Initial K.G.One panel state
+    showKGOnePanel: false,
+
     // Initial Instrument Selection panel state
     showInstrumentSelection: initialShowInstrumentSelection,
     
@@ -898,7 +907,12 @@ export const useProjectStore = create<ProjectState>((set, get) => {
     
     toggleChatBox: () => {
       const { showChatBox } = get();
-      set({ showChatBox: !showChatBox });
+      set({ showChatBox: !showChatBox, showKGOnePanel: false });
+    },
+
+    toggleKGOnePanel: () => {
+      const { showKGOnePanel } = get();
+      set({ showKGOnePanel: !showKGOnePanel, showChatBox: false });
     },
 
     // Instrument selection panel actions