feat(examples-chat): Phase 6 — timeline / time travel

[blove]

Summary

• Adds a palette toggle ("Timeline on/off") to the demo control palette, persisted to localStorage under the timeline key
• When toggled on, mounts a fixed right-side panel containing <chat-timeline-slider> from @ngaf/chat
• The slider lets users scrub through conversation checkpoints, then:
  • Replay — re-runs the graph from the selected checkpoint with no new input via agent.submit(null, { checkpointId })
  • Fork — creates a new thread via POST http://localhost:2024/threads, switches threadIdSignal to the new thread id, persists it, then replays from that checkpoint against the new thread

The <chat-timeline-slider> primitive is already shipped in @ngaf/chat; this PR only wires it into the demo shell.

Changes

• demo-shell.component.ts — adds timelineOpen signal, onTimelineChange, onTimelineReplay, onTimelineFork handlers; imports ChatTimelineSliderComponent
• control-palette.component.ts + .html — adds timelineOpen required input + timelineOpenChange output + toggle button matching existing "Debug" button style
• demo-shell.component.html — wires timeline inputs/outputs on <app-control-palette>; conditionally renders timeline panel
• demo-shell.component.css — .demo-shell__timeline-panel: fixed, right: 16px, top: 80px, bottom: 96px, width: 280px
• palette-persistence.service.ts — adds timeline?: boolean | null to PaletteState
• examples/chat/smoke/CHECKLIST.md — fills in the "Time travel / timeline" section with 14 manual checks

Test plan

• nx run-many -t test,lint,build -p examples-chat-angular — all green (9 tests pass, lint clean, build succeeds)
• Manual: palette toggle appears; panel mounts/unmounts; replay and fork work against a running LangGraph server on :2024
• Manual: timeline state persists across reload

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
cacheplane	Ready	Preview, Comment	May 10, 2026 8:41pm