feat(ui,api): chat view with live tail and autoscroll, conversation rail with last message previews

ui/src/routes/conversations/+layout.svelte

@@ -0,0 +1,27 @@
+<script lang="ts">
+  import { page } from "$app/state";
+  import ConversationList from "$lib/components/conversation-list.svelte";
+  import { cn } from "$lib/utils";
+
+  let { children } = $props();
+
+  const selected = $derived(page.params.id ?? null);
+</script>
+
+<svelte:head><title>Conversations · Beaver</title></svelte:head>
+
+<div class="grid min-h-0 flex-1 grid-cols-1 lg:grid-cols-[22rem_minmax(0,1fr)]">
+  <div
+    class={cn(
+      "min-h-0 border-r bg-sidebar/40",
+      selected ? "hidden lg:block" : "block"
+    )}
+  >
+    <ConversationList {selected} />
+  </div>
+  <div
+    class={cn("min-h-0", selected ? "flex flex-col" : "hidden lg:flex lg:flex-col")}
+  >
+    {@render children()}
+  </div>
+</div>