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/NavSessions.tsx

@@ -40,7 +40,9 @@ export function NavSessions({ sessions, activeSessionId, onOpenPanel, menuFor }:
               }}
               className={[
                 "group flex w-full cursor-pointer items-center gap-2 rounded-md px-2 py-1 text-left transition-colors focus:outline-none focus-visible:ring-2 focus-visible:ring-ring/40",
-                active ? "bg-[oklch(var(--primary)/0.12)]" : "hover:bg-accent",
+                // The in-progress (active) session is marked in yellow — both its dot
+                // and its row background — so it stands out from the rest of the rail.
+                active ? "bg-[oklch(var(--warning)/0.22)]" : "hover:bg-accent",
               ].join(" ")}
             >
               <span
@@ -48,17 +50,19 @@ export function NavSessions({ sessions, activeSessionId, onOpenPanel, menuFor }:
                 title={s.status}
                 className={[
                   "size-1.5 shrink-0 rounded-full",
-                  s.status === "open"
-                    ? "bg-[oklch(var(--success))]"
-                    : s.status === "finalized"
-                      ? "bg-primary"
-                      : "bg-muted-foreground/50",
+                  active
+                    ? "bg-[oklch(var(--warning))]"
+                    : s.status === "open"
+                      ? "bg-[oklch(var(--success))]"
+                      : s.status === "finalized"
+                        ? "bg-primary"
+                        : "bg-muted-foreground/50",
                 ].join(" ")}
               />
               <span
                 className={[
                   "min-w-0 flex-1 truncate text-[0.8rem] leading-snug",
-                  active ? "font-semibold text-primary" : "font-medium text-foreground/90",
+                  active ? "font-semibold text-foreground" : "font-medium text-foreground/90",
                 ].join(" ")}
               >
                 {label}