feat(shell): yellow active session, growing composer, phase title, refined activity log, arrow panel toggle

Fix six GUI defects, verified live against the real stack:

- NavSessions: mark the in-progress (active) session in yellow (warning
  token) — both its status dot and its row background.
- SteerInput: the composer is now an auto-growing textarea that wraps and
  grows vertically (caps at 160px, then scrolls); Enter sends, Shift+Enter
  inserts a newline.
- WorkflowBar: show a synthetic title of the current phase under the 8 dots
  from static EN/IT strings (no LLM); English is displayed to match the chrome.
- CentralStatus: reformat the 5-line system-message tail as a structured,
  monospace list with per-line markers and an emphasized last line.
- AppShell + CentralStatus: move the left Model-activity panel toggle off the
  working spinner (now a pure status indicator) onto a dedicated arrow button
  (→ opens, ← closes).
- gate: rename the phase-confirm button "Conferma e prosegui" → "Salva e
  procedi" (builders.js + its L1 test).

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

frontend/src/shell/SteerInput.tsx

@@ -1,5 +1,5 @@
 // frontend/src/shell/SteerInput.tsx
-import { useState } from "react";
+import { useEffect, useRef, useState } from "react";
 import { CornerDownLeft } from "lucide-react";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import { postSteer, createSession } from "../api/sessions";
@@ -18,7 +18,7 @@ interface Props {
   /** Interrupt the running session, persisting its state. */
   onStop?: () => void;
   /** Lets the parent focus the composer (e.g. on "New session"). */
-  inputRef?: React.Ref<HTMLInputElement>;
+  inputRef?: React.Ref<HTMLTextAreaElement>;
 }
 
 export function SteerInput({ sessionId, onSessionCreated, onStop, inputRef }: Props) {
@@ -26,6 +26,23 @@ export function SteerInput({ sessionId, onSessionCreated, onStop, inputRef }: Pr
   const [busy, setBusy] = useState(false);
   const setLastUserEntry = useSessionStore((s) => s.setLastUserEntry);
   const setPhase = useSessionStore((s) => s.setPhase);
+  const taRef = useRef<HTMLTextAreaElement | null>(null);
+
+  // Merge our own ref (for autosizing) with the forwarded one (parent focus).
+  function attachRef(el: HTMLTextAreaElement | null) {
+    taRef.current = el;
+    if (typeof inputRef === "function") inputRef(el);
+    else if (inputRef) (inputRef as React.MutableRefObject<HTMLTextAreaElement | null>).current = el;
+  }
+
+  // Grow the textarea to fit its content (up to a cap, then it scrolls), and shrink
+  // back when the text is cleared. Runs after every value change so height tracks text.
+  useEffect(() => {
+    const el = taRef.current;
+    if (!el) return;
+    el.style.height = "auto";
+    el.style.height = `${Math.min(el.scrollHeight, 160)}px`;
+  }, [text]);
 
   async function submit() {
     const trimmed = text.trim();
@@ -46,15 +63,16 @@ export function SteerInput({ sessionId, onSessionCreated, onStop, inputRef }: Pr
     }
   }
 
-  function handleKeyDown(e: React.KeyboardEvent<HTMLInputElement>) {
-    if (e.key === "Enter") {
+  function handleKeyDown(e: React.KeyboardEvent<HTMLTextAreaElement>) {
+    // Enter sends; Shift+Enter inserts a newline (the textarea grows to fit it).
+    if (e.key === "Enter" && !e.shiftKey) {
       e.preventDefault();
       submit();
     }
   }
 
   return (
-    <div className="flex items-center gap-2">
+    <div className="flex items-end gap-2">
       {sessionId && (
         <button
           type="button"
@@ -66,15 +84,15 @@ export function SteerInput({ sessionId, onSessionCreated, onStop, inputRef }: Pr
           <span className="block size-2.5 rounded-full bg-primary" />
         </button>
       )}
-      <input
-        ref={inputRef}
-        type="text"
+      <textarea
+        ref={attachRef}
+        rows={1}
         value={text}
         onChange={(e) => setText(e.target.value)}
         onKeyDown={handleKeyDown}
         placeholder={sessionId ? "Free steering (!)…" : "Ask a question to start a new session…"}
         aria-label={sessionId ? "Steering" : "New question"}
-        className="flex-1 bg-transparent px-1 text-sm outline-none placeholder:text-muted-foreground"
+        className="max-h-40 flex-1 resize-none bg-transparent px-1 py-1 text-sm leading-relaxed outline-none placeholder:text-muted-foreground"
       />
       <button
         type="button"