feat(workflow-bar): processing-only elapsed timer + optimistic phase paint on resume

Timer now accumulates only while the harness works, pausing while a gate awaits
the reviewer and freezing when finalized (keyed per session, in-memory). Resume
now colours the re-entry phase immediately from the manifest's phase (1..8),
mirroring the F1 paint for new questions.

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

frontend/src/shell/WorkflowBar.tsx

@@ -27,12 +27,14 @@ const DOT: Record<DotState, string> = {
 
 export function WorkflowBar({
   finalized = false,
-  createdAt = null,
-  updatedAt = null,
+  running = false,
+  resetKey = null,
 }: {
   finalized?: boolean;
-  createdAt?: string | null;
-  updatedAt?: string | null;
+  /** The harness/model is actively working (drives the processing timer). */
+  running?: boolean;
+  /** Active session id — remounts the timer (resets it) when the session changes. */
+  resetKey?: string | null;
 }) {
   const currentPhase = useSessionStore((s) => s.currentPhase);
   const phaseError = useSessionStore((s) => s.phaseError);
@@ -96,7 +98,7 @@ export function WorkflowBar({
         );
       })}
       </nav>
-      <ElapsedTimer startedAt={createdAt} stoppedAt={finalized ? updatedAt : null} />
+      <ElapsedTimer key={resetKey ?? "none"} running={running} />
     </div>
   );
 }