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/core/config/ConfigManager.ts

@@ -34,6 +34,10 @@ interface AppConfig {
     soundfont: {
       base_url: string;
     };
+    kgone: {
+      enabled: boolean;
+      base_url: string;
+    };
   };
   hotkeys: {
     main: {
@@ -100,6 +104,7 @@ export class ConfigManager {
   private config: AppConfig;
   private storage: KGConfigStorage;
   private isInitialized: boolean = false;
+  private kgoneServerManaged: boolean = false;
   private defaultConfig: AppConfig | null = null;
   private changeListeners: Set<(changedKeys: string[]) => void> = new Set();
 
@@ -199,6 +204,10 @@ export class ConfigManager {
           },
           soundfont: {
             base_url: 'https://cdn.jsdelivr.net/npm/soundfont-for-samplers/FluidR3_GM/'
+          },
+          kgone: {
+            enabled: false,
+            base_url: 'http://127.0.0.1:8000'
           }
         },
         hotkeys: {
@@ -548,6 +557,21 @@ export class ConfigManager {
     return copied;
   }
 
+  /**
+   * Called at startup when kgone-server.txt is found.
+   * Forces enabled=true and overrides base_url in-memory only (not persisted).
+   */
+  public setKGOneManagedByServer(url: string): void {
+    this.kgoneServerManaged = true;
+    this.setInObject(this.config as Record<string, unknown>, 'general.kgone.enabled', true);
+    this.setInObject(this.config as Record<string, unknown>, 'general.kgone.base_url', url);
+    this.notifyChangeListeners(['general.kgone.enabled', 'general.kgone.base_url']);
+  }
+
+  public isKGOneServerManaged(): boolean {
+    return this.kgoneServerManaged;
+  }
+
   /**
    * Get the default configuration
    */