Stability checkpoint Java — runbooks + FR sync + dashboards + renovate base + banner

Achievements vs stable-v1.2.0 :
- 3 SLO runbooks (availability + latency + enrichment) — unblocks Alertmanager 404s
- README.fr.md fully synced with EN (TL;DR + senior architect matrix + URL fixes)
- banner.svg refreshed (mention polyrepo + 3 SLOs as code + LTS path)
- Renovate consolidated via shared base preset + sync script
- Shared submodule SHA bumped : 3 new dashboards (SLO breakdown, latency heatmap,
  Apdex) + SLO review cadence doc + renovate-base.json

Validation : main pipeline #852 green sha=6e2a68c3f12c58c2786739e6cf7ebe0cd3c77088