Fix webmanifest

simplenotes-app/src/main/kotlin/be/simplenotes/app/filters/ImmutableFilter.kt

@@ -3,9 +3,13 @@ package be.simplenotes.app.filters
 import org.http4k.core.Filter
 import org.http4k.core.HttpHandler
 import org.http4k.core.Request
+import org.http4k.core.Status.Companion.OK
 
 object ImmutableFilter : Filter {
     override fun invoke(next: HttpHandler) = { request: Request ->
-        next(request).header("Cache-Control", "public, max-age=31536000, immutable")
+        val res = next(request)
+        if (res.status == OK)
+            res.header("Cache-Control", "public, max-age=31536000, immutable")
+        else res
     }
 }

simplenotes-app/src/main/kotlin/be/simplenotes/app/routes/Router.kt

@@ -32,7 +32,13 @@ class Router(
         val basicRoutes =
             routes(
                 "/health" bind GET to healthCheckController::healthCheck,
-                ImmutableFilter.then(static(Classpath("/static"), "woff2" to ContentType("font/woff2")))
+                ImmutableFilter.then(
+                    static(
+                        Classpath("/static"),
+                        "woff2" to ContentType("font/woff2"),
+                        "webmanifest" to ContentType("application/manifest+json")
+                    )
+                )
             )
 
         val publicRoutes = routes(