[deferred] JOURNAL-001: Typed mission journal (children of #262)

[mrnicholasbcarter-code]

Scope (minimum v1)

Typed mission events for: stage started/completed/failed, checkpoint committed, failover, verification, completion. Reuses the existing ReceiptStore.append_event seam (PR #22 already established).

Do not duplicate

This issue extends #228 VER-011 Append-only EvidenceChain & portable receipts (in code as receipt_store.append_event). JOURNAL-001 adds mission-level grouping and Cockpit-ready taxonomy.

Deferred (per audit, not for V1)

• Cockpit analytics
• Counterfactual replay UI
• Per-step strategy alternatives

Refs: evidence/V1_READINESS_AUDIT_2026-08-03.md #228