fix: reset LastUpdatedAt on restore so UI shows fresh activity time

Sessions in the poll-then-resume path showed stale "494m ago" in the
sidebar because LastUpdatedAt is only updated by SDK events, which do
not arrive during the polling window (no SDK connection).

Reset LastUpdatedAt to DateTime.Now when marking a session as actively
processing during restore.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: PureWeen

PolyPilot/Services/CopilotService.Persistence.cs

@@ -671,6 +671,11 @@ public async Task RestorePreviousSessionsAsync(CancellationToken cancellationTok
                                     capturedState.IsMultiAgentSession = IsSessionInMultiAgentGroup(capturedName);
                                     capturedState.Info.ProcessingPhase = 3; // Working
                                     capturedState.Info.ProcessingStartedAt = DateTime.UtcNow;
+                                    // Reset LastUpdatedAt so the UI doesn't show stale "Xm ago" from
+                                    // a previous app instance. Without this, sessions show "494m ago"
+                                    // because LastUpdatedAt is only updated by SDK events (which don't
+                                    // arrive during the poll-then-resume window).
+                                    capturedState.Info.LastUpdatedAt = DateTime.Now;
                                     StartProcessingWatchdog(capturedState, capturedName);
                                     NotifyStateChanged();
                                 });