feat(mobile): show relative timestamp on inbox signal cards

[Gilbert09]

Summary

Ports #2240 ("feat(inbox): show relative timestamp on signal cards") to the mobile app. Each signal card on the report detail screen now shows a short relative timestamp (e.g. 2h ago, 3d ago) in the header, derived from the signal's own timestamp.

Reuses the existing formatRelativeTime util from @/lib/format instead of introducing a new component — the desktop's <RelativeTimestamp /> wrapper exists primarily to add a tooltip with the full date, which has no native equivalent on mobile.

Test plan

• Open a signal report on the mobile app and expand the Signals section
• Confirm each signal card shows a relative timestamp (e.g. 5m ago, 2h ago) on the right side of the header
• Confirm the timestamp wraps cleanly alongside the source-line label and the verified badge (no overflow)
• Confirm cards with a missing/invalid signal.timestamp simply omit the timestamp (no crash, no NaN)

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
apps/mobile/src/features/inbox/components/SignalCard.tsx:211-212
`formatRelativeTime` performs no bounds-check on negative differences. If `signal.timestamp` is a valid but future date (e.g., due to clock skew or a bad server timestamp), `diffMs` is negative, and the first branch (`diffSec < 60`) passes for any difference up to 60 seconds in the future, returning `"just now"`. Beyond that, the function falls through to `return \`${diffMin}m ago\`` with `diffMin` being a large negative integer — so the card would show something like `-120m ago`. A simple pre-render clamp on `hasTimestamp` keeps the output sensible.

```suggestion
  const timestampMs = signal.timestamp ? Date.parse(signal.timestamp) : NaN;
  const hasTimestamp = !Number.isNaN(timestampMs) && timestampMs <= Date.now();
```

_{Reviews (1): Last reviewed commit: "feat(mobile): show relative timestamp on..." | Re-trigger Greptile}

[greptile-apps]

formatRelativeTime performs no bounds-check on negative differences. If signal.timestamp is a valid but future date (e.g., due to clock skew or a bad server timestamp), diffMs is negative, and the first branch (diffSec < 60) passes for any difference up to 60 seconds in the future, returning "just now". Beyond that, the function falls through to return \${diffMin}m ago`withdiffMinbeing a large negative integer — so the card would show something like-120m ago. A simple pre-render clamp on hasTimestamp` keeps the output sensible.

Suggested change

	const timestampMs = signal.timestamp ? Date.parse(signal.timestamp) : NaN;
	const hasTimestamp = !Number.isNaN(timestampMs);
	const timestampMs = signal.timestamp ? Date.parse(signal.timestamp) : NaN;
	const hasTimestamp = !Number.isNaN(timestampMs) && timestampMs <= Date.now();

Prompt To Fix With AI

This is a comment left during a code review.
Path: apps/mobile/src/features/inbox/components/SignalCard.tsx
Line: 211-212

Comment:
`formatRelativeTime` performs no bounds-check on negative differences. If `signal.timestamp` is a valid but future date (e.g., due to clock skew or a bad server timestamp), `diffMs` is negative, and the first branch (`diffSec < 60`) passes for any difference up to 60 seconds in the future, returning `"just now"`. Beyond that, the function falls through to `return \`${diffMin}m ago\`` with `diffMin` being a large negative integer — so the card would show something like `-120m ago`. A simple pre-render clamp on `hasTimestamp` keeps the output sensible.

```suggestion
  const timestampMs = signal.timestamp ? Date.parse(signal.timestamp) : NaN;
  const hasTimestamp = !Number.isNaN(timestampMs) && timestampMs <= Date.now();
```

How can I resolve this? If you propose a fix, please make it concise.

[github-actions]

Simple UI addition showing a relative timestamp on signal cards. The bot's concern about future timestamps is already addressed in the diff with the timestampMs <= Date.now() guard.