feat(caddy,stand,smoke): prod-like routing stand, api smoke, old ui fallback for unknown paths

src/routes/+error.svelte

@@ -0,0 +1,29 @@
+<script lang="ts">
+  import { oldUiUrl } from "#lib/spa-paths.js";
+  import { page } from "$app/state";
+
+  const NOT_FOUND = 404;
+
+  const missing = $derived(page.status === NOT_FOUND);
+
+  $effect(() => {
+    if (missing) {
+      location.replace(oldUiUrl(page.url.href));
+    }
+  });
+</script>
+
+{#if missing}
+  <p class="p-6 text-cladd-fg-soft">Opening this page in the old interface</p>
+{:else}
+  <div class="flex flex-col gap-2 p-6">
+    <h1 class="font-semibold text-[18px]">Something went wrong</h1>
+    <p class="text-cladd-fg-soft">{page.error?.message}</p>
+    <a
+      class="text-brand underline"
+      data-sveltekit-reload
+      href={oldUiUrl(page.url.href)}
+      >Open this page in the old interface</a
+    >
+  </div>
+{/if}

src/routes/+layout.svelte

@@ -43,10 +43,12 @@
         return;
       }
       lastHref = url.href;
-      if (fromUrl?.start === start && fromUrl?.end === end) {
+      const clean = !url.searchParams.has("ffui");
+      if (clean && fromUrl?.start === start && fromUrl?.end === end) {
         return;
       }
       const next = new URL(url.href);
+      next.searchParams.delete("ffui");
       next.searchParams.set("start", start);
       next.searchParams.set("end", end);
       lastHref = next.href;