List Shared Data Heartbeat Logs

Return heartbeat scheduler runs with their content fields.

The non-consent variant /admin/users/{id}/heartbeat-logs returns only metadata (id, action_type, channel, created_at) since #336. For consenting users the full content surfaces here: message_text (what the agent sent on this tick), reasoning (why it sent / skipped — often quotes the user back to themselves), and tasks (the serialized task state the LLM was deciding from). All three columns are envelope-encrypted at rest; ORM reads decrypt transparently and we redact PII shapes before serialization.