fix: normalize JS static MIME types on Windows

Refs #802

app.py

@@ -1,6 +1,23 @@
 # app.py — slim orchestrator
+import mimetypes
 import os
 
+
+def register_static_mime_types() -> None:
+    """Force stable JS module MIME types across platforms.
+
+    Some native Windows setups inherit stale/incorrect registry mappings for
+    ``.js``/``.mjs``, which can make Starlette serve ES modules with a non-JS
+    ``Content-Type`` and cause the UI to load but fail on click. Re-register the
+    standard MIME types at startup so static assets are served consistently.
+    """
+
+    mimetypes.add_type("text/javascript", ".js")
+    mimetypes.add_type("application/javascript", ".mjs")
+
+
+register_static_mime_types()
+
 # Windows: force HuggingFace/fastembed to COPY model files instead of symlinking.
 # On a network-share/UNC data dir Windows can't follow HF's symlinks ([WinError
 # 1463]), so the ONNX embedding model fails to load. huggingface_hub reads this