feat(shell): 30/55/15 layout, formatted activity log, instant resume, stop confirmation

Left panels 30vw / central 55% / right rail 15vw, minimal padding. Model-activity
log and documents render via .thot-prose; decisions become hairline rows with
semantic type chips. Resume switches the view optimistically (instant feedback).
The Stop button now asks for confirmation before interrupting.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/shell/ModelActivityPanel.tsx

@@ -30,8 +30,8 @@ export function ModelActivityPanel({ onClose }: { onClose: () => void }) {
   const source = shown.join("\n\n");
 
   return (
-    <aside className="flex w-[380px] shrink-0 flex-col border-r border-border bg-sidebar">
-      <div className="flex items-center justify-between border-b border-border/70 px-4 py-3">
+    <aside className="flex w-[30vw] max-w-[30vw] shrink-0 flex-col border-r border-border bg-sidebar">
+      <div className="flex items-center justify-between border-b border-border/70 px-3 py-3">
         <h2 className="font-heading text-sm font-semibold text-foreground">Model activity</h2>
         <div className="flex items-center gap-1">
           {canExpand && (
@@ -50,11 +50,11 @@ export function ModelActivityPanel({ onClose }: { onClose: () => void }) {
           </Button>
         </div>
       </div>
-      <div className="flex-1 overflow-y-auto px-4 py-4">
+      <div className="flex-1 overflow-y-auto px-3 py-5">
         {shown.length === 0 ? (
           <p className="text-sm text-muted-foreground">No activity yet.</p>
         ) : (
-          <div className="prose prose-sm dark:prose-invert max-w-none text-foreground/90">
+          <div className="thot-prose max-w-[74ch]">
             <ReactMarkdown remarkPlugins={[remarkGfm]}>{source}</ReactMarkdown>
           </div>
         )}