Keep focused agent timelines live and catch up instantly (#2196)

* fix(app): keep focused agent timelines live

Window focus was conflated with app visibility, so switching OS windows could remove the selected timeline subscription. Separate those signals, grace every visibility-driven removal, and cover retained history until authoritative catch-up completes.

* fix(app): keep timeline catch-up failures non-blocking

* fix(app): surface timeline catch-up failures

* fix(app): preserve file preview refocus

* fix(app): preserve optimistic catch-up flow

packages/app/src/components/terminal-pane-focus-claim.test.ts

@@ -18,14 +18,14 @@ describe("terminal pane focus claim", () => {
   it("waits for both the client and renderer before requesting a claim", () => {
     const withoutClient = canRequestFocusClaim({
       isWorkspaceFocused: true,
-      isAppVisible: true,
+      isAppActivelyVisible: true,
       isClientReady: false,
       isConnected: true,
       isRendererReady: true,
     });
     const withoutRenderer = canRequestFocusClaim({
       isWorkspaceFocused: true,
-      isAppVisible: true,
+      isAppActivelyVisible: true,
       isClientReady: true,
       isConnected: true,
       isRendererReady: false,
@@ -37,7 +37,7 @@ describe("terminal pane focus claim", () => {
   it("does not deliver a requested claim after the host disconnects", () => {
     const disconnected = canRequestFocusClaim({
       isWorkspaceFocused: true,
-      isAppVisible: true,
+      isAppActivelyVisible: true,
       isClientReady: true,
       isConnected: false,
       isRendererReady: true,