fix: optimistic archiving/closing and tab UX improvements

- Archive agents optimistically on close with rollback on error
- Close tabs immediately instead of waiting for RPC response
- Kill terminals in background with cache invalidation on failure
- Bulk close fires RPC in background, closes all tabs upfront
- Move new-tab button out of scroll area, rename to "New agent tab"
- Support invalidateQueries option in applyArchivedAgentCloseResults
- Fix workspace descriptor id/projectId types (string not number)

packages/app/src/hooks/use-archive-agent.test.ts

@@ -139,4 +139,36 @@ describe("useArchiveAgent", () => {
       entries: [{ agent: { id: "agent-2" } }],
     });
   });
+
+  it("can apply archived agent close results without invalidating cached lists", () => {
+    const queryClient = new QueryClient();
+    useSessionStore
+      .getState()
+      .initializeSession("server-a", {} as DaemonClient);
+    useSessionStore.getState().setAgents(
+      "server-a",
+      new Map([
+        [
+          "agent-1",
+          makeAgent(),
+        ],
+      ]),
+    );
+    queryClient.setQueryData(["sidebarAgentsList", "server-a"], {
+      entries: [{ agent: { id: "agent-1" } }, { agent: { id: "agent-2" } }],
+    });
+    queryClient.setQueryData(["allAgents", "server-a"], {
+      entries: [{ agent: { id: "agent-1" } }, { agent: { id: "agent-2" } }],
+    });
+
+    applyArchivedAgentCloseResults({
+      queryClient,
+      serverId: "server-a",
+      results: [{ agentId: "agent-1", archivedAt: "2026-04-01T04:00:00.000Z" }],
+      invalidateQueries: false,
+    });
+
+    expect(queryClient.getQueryState(["sidebarAgentsList", "server-a"])?.isInvalidated).toBe(false);
+    expect(queryClient.getQueryState(["allAgents", "server-a"])?.isInvalidated).toBe(false);
+  });
 });