feat(web): new task opens straight into chat, context rail waits for content, frosted windows

New Task now opens directly as an empty ChatThread (NewTaskChat) instead of
a separate compose screen, sized like a real task window. The Scope/Activity
context rail in a task window no longer renders until there's actually
something to show (touched entities, activity, or an open question),
avoiding an empty-placeholder sidebar on every new task. Also fixes the
chat input defaulting to several lines tall on window open, centers the
empty-chat greeting vertically, and gives floating windows the same
frosted-glass look as the desktop's task launcher card.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/lib/components/ChatThread.svelte

@@ -100,13 +100,15 @@
   })
   const inputMinSize = $derived(threadHeight > 0 ? (oneLinePx / threadHeight) * 100 : 12)
 
+  // Keep the input pinned to inputMinSize (one line) until the user actually
+  // drags the splitter — not just on the first measurement. A floating
+  // window's threadHeight is 0/wrong for a frame or two while it animates
+  // open, and locking the percentage to that first reading left the input
+  // several lines tall once the window reached full size (fixed 2026-07-21).
   let inputSize = $state(12)
-  let inputSizeDefaulted = false
+  let userResizedInput = false
   $effect(() => {
-    if (!inputSizeDefaulted && threadHeight > 0) {
-      inputSize = inputMinSize
-      inputSizeDefaulted = true
-    }
+    if (!userResizedInput) inputSize = inputMinSize
   })
 
   function isNearBottom(): boolean {
@@ -172,12 +174,12 @@
 </script>
 
 <div class="flex h-full min-h-0 min-w-0 flex-col" bind:clientHeight={threadHeight}>
-  <Splitpanes horizontal theme="oikos-theme" dblClickSplitter={false} class="min-h-0 flex-1">
+  <Splitpanes horizontal theme="oikos-theme" dblClickSplitter={false} class="min-h-0 flex-1" on:resize={() => (userResizedInput = true)}>
     <Pane class="flex flex-col">
   <div class="min-h-0 flex-1 overflow-y-auto" bind:this={container} onscroll={onScroll}>
-    <div class="mx-auto flex max-w-3xl flex-col gap-5 p-4">
+    <div class="mx-auto flex min-h-full max-w-3xl flex-col gap-5 p-4">
       {#if messages.length === 0}
-        <div class="flex flex-col items-center gap-6 pt-24 text-center">
+        <div class="flex flex-1 flex-col items-center justify-center gap-6 text-center">
           <div>
             <h2 class="text-xl font-semibold">Nomos</h2>
             <p class="mt-1 text-sm text-muted-foreground">Your resident operator. Ask about the fleet, or tell it to act.</p>