Stability checkpoint Java — governance + dashboards in repo + ADR-0058/59 + PROD-READINESS + chaos demo

Achievements vs stable-v1.2.1 :
- .gitlab/CODEOWNERS (renovate auto-assignee)
- 3 NEW Grafana dashboards moved to OWN repo (Java-specific Micrometer metrics) :
  - infra/observability/grafana-dashboards/slo-breakdown-by-endpoint.json
  - infra/observability/grafana-dashboards/latency-heatmap.json
  - infra/observability/grafana-dashboards/apdex.json
- Sloth PrometheusRule moved IN repo : deploy/kubernetes/observability-prom/mirador-slo.yaml
- wrap-as-prometheusrule.py updated to write LOCAL not SHARED
- Cosign verify identity regex bumped for new project URL
- Shared submodule SHA bumped (multiple) :
  - ADR-0058 SLO/SLA via Sloth
  - ADR-0059 renovate base preset workflow
  - PRODUCTION-READINESS.md cross-cutting checklist
  - SLO Overview cross-cutting Grafana dashboard
  - SLO review cadence doc
  - bin/dev/burn-slo-budget.sh chaos demo script
  - docs/demo/live-demo.md interview playbook
  - .gitlab/CODEOWNERS + CHANGELOG + CONTRIBUTING + SECURITY in shared
  - Repo-specific dashboards moved out of shared (per scope discipline)

Validation : main pipeline #859 green sha=57e10b8f55c3d9fd726db2fd30715b12e46e39a9