Switch model URLs from GitHub Releases to raw.githubusercontent.com

GitHub Releases don't serve CORS headers, so browser fetch() fails
under COEP. raw.githubusercontent.com serves both:
- Access-Control-Allow-Origin: *
- Cross-Origin-Resource-Policy: cross-origin

Model files are hosted on the orphan `models` branch and served via:
https://raw.githubusercontent.com/CSSLab/maia-platform-frontend/models/

https://claude.ai/code/session_01T73Yphu4y2U3c3ctCcHVPf

Author: claude

src/contexts/MaiaEngineContext.tsx

@@ -33,7 +33,7 @@ export const MaiaEngineContextProvider: React.FC<{ children: ReactNode }> = ({
     const model = new Maia({
       model:
         process.env.NEXT_PUBLIC_MAIA_MODEL_URL ??
-        'https://github.com/CSSLab/maia-platform-frontend/releases/download/models-v1/maia_rapid.onnx',
+        'https://raw.githubusercontent.com/CSSLab/maia-platform-frontend/models/maia2/maia_rapid.onnx',
       setStatus: setStatus,
       setProgress: setProgress,
       setError: setError,

src/lib/engine/stockfish.ts

@@ -350,11 +350,12 @@ const setupStockfish = (): Promise<StockfishWeb> => {
           locateFile: (name: string) => `/stockfish/${name}`,
         })
         .then(async (instance: StockfishWeb) => {
-          // NNUE weights are hosted on GitHub Releases to avoid Vercel bandwidth costs.
+          // NNUE weights are hosted on a separate branch and served via
+          // raw.githubusercontent.com (CORS + COEP compatible).
           // Override with NEXT_PUBLIC_STOCKFISH_NNUE_BASE_URL for self-hosted deployments.
           const nnueBaseUrl =
             process.env.NEXT_PUBLIC_STOCKFISH_NNUE_BASE_URL ??
-            'https://github.com/CSSLab/maia-platform-frontend/releases/download/models-v1'
+            'https://raw.githubusercontent.com/CSSLab/maia-platform-frontend/models/stockfish'
           // Load NNUE models before resolving
           Promise.all([
             fetch(`${nnueBaseUrl}/${instance.getRecommendedNnue(0)}`),