fix: revert heartbeat_interval change breaking docket worker (#669)
The 30s heartbeat_interval added in #653 broke background task execution.
Likes scheduled since Dec 29 deploy have null atproto_like_uri.
Reverts the Docket heartbeat_interval back to default (2s).
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Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
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