fix: locateFile cho FluidSynth WASM module (dùng self-host/CDN)

Module script (type=module) có document.currentScript === null,
nên libfluidsynth không thể tự locate .wasm file. Fix: pass
locateFile() trả về URL .wasm tương ứng với URL .js đã load.

fluidsynthLoader.js: expose __FluidSynthLocateWasm() trả về
FLUIDSYNTH_JS_URL.replace('.js', '.wasm'). Dùng polling
setInterval thay vì resolve callback cho đáng tin cậy hơn.
soundfontPlayer.js: pass locateFile factory khi gọi factory.

app/static/js/services/soundfontPlayer.js

@@ -73,7 +73,14 @@
                     }
 
                     console.log("[SonicSF] Initializing FluidSynth WASM Engine...");
-                    _fluidModule = await window.__FluidSynthModuleFactory();
+                    _fluidModule = await window.__FluidSynthModuleFactory({
+                        locateFile: function (path) {
+                            if (path.endsWith('.wasm')) {
+                                return window.__FluidSynthLocateWasm ? window.__FluidSynthLocateWasm() : path;
+                            }
+                            return path;
+                        }
+                    });
 
                     if (!_fluidModule || !_fluidModule._new_fluid_settings) {
                         throw new Error("FluidSynth WASM module loaded but API missing");