fix(app): paginate canonical timeline catch-up to avoid relay 1009 disconnect loop (#657)

@fireblue diagnosed the production failure mode: long canonical timeline catch-up could exceed the relay WebSocket frame cap, close with 1009, and send clients into a reconnect loop. Their seatbelt fix also removed the `limit: 0` footgun that let app callers request an unbounded frame.

This maintainer pass keeps that diagnosis and redirects the UX around bounded projected pages:

- initial agent load fetches the latest canonical tail
- app resume/reconnect re-fetches the latest tail instead of chaining after-cursor pages
- in-stream gaps still use bounded after-cursor catch-up
- older history loads explicitly when the user scrolls to the oldest edge
- shared page size is TIMELINE_FETCH_PAGE_SIZE = 100 projected timeline items, matching the daemon's canonical projection semantics rather than raw delta chunks

Original diagnosis and fix by @fireblue.

Co-authored-by: Mohamed Boudra <boudra.moha@gmail.com>

packages/app/src/components/agent-stream-view.test.tsx

@@ -19,8 +19,12 @@ const mockSessionState = vi.hoisted(() => ({
       client: null,
       agentStreamHead: new Map<string, StreamItem[]>(),
       workspaces: new Map(),
+      agentTimelineCursor: new Map(),
+      agentTimelineHasOlder: new Map(),
+      agentTimelineOlderFetchInFlight: new Map(),
     },
   },
+  setAgentTimelineOlderFetchInFlight: () => {},
 }));
 
 vi.mock("react-native-unistyles", () => ({