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/AppShell.tsx

@@ -8,6 +8,7 @@ import { SessionMenu } from "./SessionMenu";
 import { SessionDocumentsPanel } from "./SessionDocumentsPanel";
 import { RenameDialog } from "./RenameDialog";
 import { DeleteConfirmDialog } from "./DeleteConfirmDialog";
+import { StopConfirmDialog } from "./StopConfirmDialog";
 import { SteerInput, ComposerFooter } from "./SteerInput";
 import { WorkflowBar } from "./WorkflowBar";
 import { Pencil } from "lucide-react";
@@ -42,6 +43,7 @@ export function AppShell() {
   const [archiveOpen, setArchiveOpen] = useState(false);
   const [renameTarget, setRenameTarget] = useState<SessionSummary | null>(null);
   const [deleteTarget, setDeleteTarget] = useState<SessionSummary | null>(null);
+  const [stopConfirm, setStopConfirm] = useState(false);
   const [collapsedGroups, setCollapsedGroups] = useState<Record<string, boolean>>({});
   const [renameGroupTarget, setRenameGroupTarget] = useState<string | null>(null);
 
@@ -68,12 +70,16 @@ export function AppShell() {
     });
   }
   async function doResume(id: string) {
+    const s = sessions.find((x) => x.id === id) ?? null;
+    // Optimistic switch: change to the session view IMMEDIATELY so the click feels
+    // instant (the resume POST spawns a Pi process and can take seconds). The
+    // working spinner shows straight away; the backend calls run after.
+    setPanelSession(null);
+    resetSession();
+    setActiveSessionId(id);
     try {
       await resumeSession(id);
-      setPanelSession(null);
-      setActiveSessionId(id);
-      // Optimistic phase paint on resume: colour the re-entry phase immediately,
-      // before the first gate arrives (mirrors the F1 paint for new questions).
+      // Optimistic phase paint: colour the re-entry phase before the first gate.
       // The manifest's `phase` is the 1-based current phase (1..8).
       try {
         const m = (await getSession(id)) as { phase?: number };
@@ -84,6 +90,10 @@ export function AppShell() {
         /* non-fatal: the first gate will set the phase */
       }
     } catch {
+      // Revert the optimistic switch and restore the panel.
+      resetSession();
+      setActiveSessionId(null);
+      if (s) setPanelSession(s);
       toast.error("Failed to resume session.");
     }
   }
@@ -216,7 +226,7 @@ export function AppShell() {
                 <SteerInput
                   sessionId={activeSessionId}
                   onSessionCreated={setActiveSessionId}
-                  onStop={stopSession}
+                  onStop={() => setStopConfirm(true)}
                   inputRef={composerRef}
                 />
               </div>
@@ -227,7 +237,7 @@ export function AppShell() {
       </div>
 
       {/* Right session rail — symmetric to the portal's left sidebar */}
-      <aside className="flex w-[280px] shrink-0 flex-col border-l border-border bg-sidebar">
+      <aside className="flex w-[15vw] shrink-0 flex-col border-l border-border bg-sidebar">
         <div className="relative px-4 pb-3 pt-5 text-center">
           <h1 className="font-heading text-xl font-semibold leading-none tracking-tight text-foreground">
             Thoth<span className="text-primary">II</span>
@@ -333,6 +343,12 @@ export function AppShell() {
 
       <Toaster />
 
+      <StopConfirmDialog
+        open={stopConfirm}
+        onOpenChange={setStopConfirm}
+        onConfirm={stopSession}
+      />
+
       {renameTarget && (
         <RenameDialog
           open