fix(app): reduce workspace screen re-renders and fix archived agent handling

Replace greedy agents Map subscription with a Zustand selector that
derives workspace agent visibility (ID sets only) with custom equality,
so the workspace screen only re-renders when agents are added, removed,
or archived — not on every status/activity update.

Fix tab pruning to check against all known agents (including archived)
instead of only active agents, so archived agent tabs survive
reconciliation. Remove the auto-unarchive effect that called
refreshAgent() as a workaround. Hide input area for archived agents.

packages/app/src/panels/agent-panel.tsx

@@ -802,7 +802,7 @@ function AgentPanelBody({
             </ReanimatedAnimated.View>
           </View>
 
-          {agentId && !isArchivingCurrentAgent ? (
+          {agentId && !isArchivingCurrentAgent && !agent?.archivedAt ? (
             <AgentInputArea
               agentId={agentId}
               serverId={serverId}