QP: durable, shared job store (replace in-memory JOB_STORE)

[bjagg]

Part of the ADR-0003 epic #1105. Plan: docs/operations/proposals/advisor-qp-direct-retrieval.md (PR #1104). Decision: ADR-0003.

Goal: Move QP job state off the in-memory dict so partial state is durable and the QP can scale past one instance.

Scope:

• JOB_STORE is a module-level in-memory dict (components/lif/query_planner_service/core.py:371) → the orchestrator callback and the status poller must be the same process.
• Move to a durable/shared store; unblock multi-instance QP.

Size: M · Depends on: B