[FR-010] Maintainer can read 1-page postmortem from manifest + aggregates

[explosivebit]

Trace: PRD prd-v0-1-smoke-evaluation-run · FR-010 · SC-5 · Architect finding #7 (was unmapped)

Capability: Generator script reads manifest.json + aggregates, produces 1-page markdown per template in docs/04-runbook/12-first-smoke-run-playbook.md § Postmortem template.

Acceptance:

• SC-5: output ≤ 1 markdown page (~80 lines)
• Includes: run_hash, scope, what worked / failed, cost, latency, task issues, model/provider issues, scoring issues, changes before next run
• Output path: docs/04-runbook/post/smoke-001.md

Implementation locus: apps/eval-core-py/src/orchestrator/postmortem.py (new) + Makefile postmortem target