IJournal implementation backed by Datahike.

Stores operation executions as Datalog entities with bitemporal attributes:
- :op/tx-time     — when the operation was recorded (Datahike transaction time)
- :op/valid-time  — when the operation actually occurred (wall clock)
- :op/type        — keyword (:process/spawn, :network/connect, :shell/exec, etc.)
- :op/input       — EDN-serialized input args
- :op/output      — EDN-serialized Result (ok value or err)
- :op/duration-ms — wall-clock duration
- :op/success?    — boolean (derived from Result)
- :op/caller      — agent-id or context string
- :op/session     — session identifier
- :op/causal-prev — reference to prior operation (causal chain)

Schema is installed on first connection. Idempotent.