dlt/faultline/spike

Surface error groups that are firing right now.

1. Parse $ARGUMENTS as the lookback window. Default to 1h. Convert to an ISO 8601 timestamp for "now minus duration".
2. Call list_error_groups with since: <iso-timestamp> and the default limit. Note: since filters by last_seen_at, so this returns groups that have been hit at least once in the window — not strictly groups that "spiked", but it's the closest available signal.
3. Sort the response by occurrences_count descending and render: id | exception_class | count | first_seen_at | last_seen_at.
4. Flag any group whose first_seen_at is inside the window — those are brand-new errors that only started appearing now, which is the strongest spike signal.
5. Offer to drill into the top one with /debug <id>.

If you also want a global volume picture, suggest /stats <period> — that one shows time-bucketed counts across the whole instance.