feat: add a timeline_event transcript card

[ThomasK33]

Summary

Adds a dedicated transcript card for the timeline_event tool, which currently falls back to the generic renderer. Collapsed, the agent's one-sentence note is the summary, tagged with an ask-mode category chip. Expanded, the card previews the row exactly as it lands in the Timeline tab (ask-mode ink, Sparkles ring, category badge) under its day header, and explains where to find it.

Background

The durable workspace timeline landed in #3755/#3756 with the timeline_event tool, but calls render as generic JSON dumps in the transcript. The card design comes from the Mux Design System mockup (Timeline Event Tool Call.html), bound here to the real backend shapes rather than the mockup's idealized ones.

Implementation

• TimelineEventToolResultSchema (+ derived TimelineEventToolArgs/TimelineEventToolResult types) — the real result is { success: true, recorded: boolean }, where recorded: false means TimelineService throttled the note (duplicate or rate-limited) and nothing was written. The card surfaces that as an amber "Not recorded" chip plus an explanation instead of a preview that would overstate what happened.
• The feed-row preview is a static replica of TimelineEventRow's agent-authored variant. To keep it provably in sync with the tab, the row icon comes from the shared getTimelinePresentation("agent.event"), and the day/time formatters (getTimelineDayLabel, formatTimelineTime) are extracted from TimelinePanel.tsx into timelinePresentation.ts and used by both. The preview's day header and time cell derive from toolCallTimestamp and are omitted when unavailable — nothing is fabricated.
• Result handling follows the current card conventions: unwrapResult for the SDK JSON container, safeParse for self-healing on malformed persisted results, and both persisted error shapes ({ success: false, error } and the nested bare { error }).
• Registered in getToolComponent.ts; header icon (Sparkles, matching the feed's agent.event rows) in TOOL_NAME_TO_ICON.

Validation

• New happy-dom suite covers the behavioral branches: recorded/throttled gating, badge derivation (picked_up → "picked up", missing category → "Agent"), both error shapes, JSON-container unwrap, and timestamp gating.
• Stories mirror the design gallery (all five categories, fallback, throttled, executing, error) plus a 375px pinned-width play test asserting no horizontal overflow. Snapshots are pixel: PIXEL_DISABLED since the repo-wide budget is at its ceiling.
• Full bun test src matches the clean-main baseline exactly (the same 30 pre-existing env-dependent failures, none in touched areas); TimelinePanel's 16 jest tests and a static Storybook build pass.

Risks

Low. The card and registry entry are new code paths gated to timeline_event. The only shared-code change is moving the day/time formatters out of TimelinePanel.tsx (behavior-preserving, covered by the existing timeline jest suite).

[ThomasK33]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Another round soon, please!

Reviewed commit: 974f03b6f7

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