docs: introduce docs/archive, remove finished sprint boards and generated report

- docs/archive/2026/ with index README: DR tabletop drill, workstation
  audits, HA/Ecowitt draft, pre-Borg backup audit, finished windows
  reinstall project docs
- delete weekend sprint boards (content preserved in MASTER_TODO done log
  and git history)
- untrack generated ops/policy-checks/last-report.md and gitignore it
- fix references (CLAUDE.md, docs/README.md, ops/windows-reinstall/README.md)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CLAUDE.md

@@ -22,7 +22,7 @@ Zusaetzlich je nach Thema:
 - Secrets: `docs/SECRETS_MAP.md`
 - GitOps-/Komodo-/Runtime-Drift: `docs/GITOPS_DRIFT_RUNBOOK.md`
 - Gesamtbild fuer KI-Agenten: `docs/AI_CONTEXT.md`
-- Home Assistant / Ecowitt / InfluxDB: `docs/HOME_ASSISTANT_INFLUXDB_ECOWITT.md`
+- Architektur-/Betriebsentscheidungen mit Begruendung: `docs/DECISIONS.md`
 
 ## Projektbeschreibung