fix(ui/ux): make the browser revalidate the static files

wordarr/main.py

@@ -23,5 +23,17 @@ app.include_router(imports.router)
 app.include_router(fs.router)
 
 
+class RevalidatingStatics(StaticFiles):
+    """Without a Cache-Control header the browser caches heuristically and does
+    not ask again, so a redeployed app.js kept rendering the old UI. no-cache
+    still allows the cached copy, it just has to be revalidated first - one 304
+    per file per load."""
+
+    def file_response(self, *args, **kwargs):  # starlette passes these positionally
+        resp = super().file_response(*args, **kwargs)
+        resp.headers["Cache-Control"] = "no-cache"
+        return resp
+
+
 static_dir = Path(__file__).parent.parent / "static"
-app.mount("/", StaticFiles(directory=static_dir, html=True), name="static")
+app.mount("/", RevalidatingStatics(directory=static_dir, html=True), name="static")