Chat composer: WorkClaw bottom spacing + input height

Verified against the dark chat/welcome captures:
- Active form wrapper: pb-4 → px-4 pt-4 pb-8 + bg-gradient-to-t from-background
  to-transparent (32px bottom gap with a fade, was a flush 16px).
- Textarea: rest at 44px and grow-then-scroll via [field-sizing:content] (we
  had no auto-grow). Per-variant caps — active min-h-11 max-h-[180px], welcome
  max-h-[88px]; + pl-1. (Reviewer said keep max-h-40, but prod is 180/88, and
  field-sizing is the actual grow mechanism.)
- Box surface kept as-is (#1F1F1F + shadow) per the decision — not switching to
  WorkClaw's flat #262626.

typecheck/lint(0)/86 unit/p1-chat/6 visual green; no baseline change.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

frontend/src/components/chat/Composer.tsx

@@ -60,6 +60,10 @@ export function Composer({
     }
   }
 
+  // WorkClaw rests the active input at 44px and grows-then-scrolls via CSS
+  // field-sizing (the welcome pill rests at one line, caps lower).
+  const heightClasses =
+    variant === "active" ? "min-h-11 max-h-[180px]" : "max-h-[88px]";
   const textarea = (
     <textarea
       aria-label={`Message ${agentName}`}
@@ -70,7 +74,7 @@ export function Composer({
       rows={1}
       onChange={(e) => setValue(e.target.value)}
       onKeyDown={handleKeyDown}
-      className="max-h-40 min-h-6 w-full flex-1 resize-none bg-transparent text-sm text-foreground outline-none placeholder:text-subtle-foreground"
+      className={`${heightClasses} w-full flex-1 resize-none bg-transparent pl-1 text-sm text-foreground outline-none [field-sizing:content] placeholder:text-subtle-foreground`}
     />
   );
 
@@ -90,7 +94,10 @@ export function Composer({
   // right while generating).
   if (variant === "active") {
     return (
-      <form onSubmit={submit} className="pb-4">
+      <form
+        onSubmit={submit}
+        className="bg-gradient-to-t from-background to-transparent px-4 pt-4 pb-8"
+      >
         <div className={`flex flex-col gap-2 p-4 ${SURFACE}`}>
           {textarea}
           <div className="flex items-center gap-2">