Migrate Grafana/Prometheus/SonarQube from docker-compose to k8s (step #10)

Real data migrated, not a fresh start: 1.2GB Prometheus TSDB, Grafana's
existing dashboards/DB (its admin password was already changed from
default — confirmed real, in-use data), SonarQube's data/logs/extensions
and its own Postgres DB (confirmed: the actual `management-platform`
SonarQube project survived, matching the Jenkinsfile's own
-Dsonar.projectKey). Old docker-compose services stopped, not removed —
left as a rollback path.

Real problems hit and fixed along the way (see k8s/monitoring/README.md
for the full detail, worth reading before touching any of this again):

- k3s's bundled Traefik defaults to a LoadBalancer Service, which
  immediately hijacked ports 80/443 via iptables DNAT (klipper-lb) out
  from under this VM's existing unrelated nginx-served app ("nqks") the
  moment k3s was installed. Patched Traefik to ClusterIP via a
  HelmChartConfig; nginx now reverse-proxies the 3 new domains to
  Traefik's ClusterIP instead of Traefik touching host ports at all.

- Caught my own mistake before it caused damage: "corrected" what I
  assumed was a typo (grafanna.nav.ovh -> grafana.nav.ovh) — the two-N
  version is what the user actually specified, and is what points at this
  VM; plain grafana.nav.ovh is a different, unrelated, pre-existing live
  server at 109.199.127.74. Renamed everything back before requesting any
  cert or touching that domain.

- Adding hostPort to the SonarQube pod (for Jenkins' hardcoded
  178.18.243.51:9000) broke pod-to-pod routing to that pod entirely —
  Traefik couldn't reach it (hung/504) while direct host-to-pod and
  host-to-ClusterIP both worked fine the whole time, which is what gave
  it away. Replaced with a host-level socat proxy (systemd unit) to the
  Service's ClusterIP instead, which touches nothing pod-level. Verified
  Jenkins' exact address still works AND Traefik routing to the same pod
  works simultaneously.

- SonarQube needed a DB migration after the version jump
  (DB_MIGRATION_NEEDED), then OOM'd during post-migration rule
  re-registration on the compose file's original 256MB web heap — bumped
  SONAR_WEB_JAVAADDITIONALOPTS.

TLS: real Let's Encrypt certs via certbot (HTTP-01, nginx already owns
port 80 so no DNS-01/OVH-webhook replication needed on this second
cluster), auto-renewing. Access: HTTP Basic Auth in front of all three
domains for browser access; SonarQube also stays reachable unauthenticated
at 178.18.243.51:9000 specifically for Jenkins (which authenticates via
its own token, not BasicAuth — that path would break the scanner),
restricted to the main server's IP via ufw, not open to the internet.

Verified end-to-end: all three https://*.nav.ovh domains return 401
without credentials and load correctly with them; Jenkins' exact
SonarQube address (no auth) still returns 200; real data confirmed
present in Grafana, Prometheus, and SonarQube post-migration.

k8s/monitoring/monitoring-ingress.yaml

@@ -0,0 +1,53 @@
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: grafana
+  namespace: monitoring
+spec:
+  ingressClassName: traefik
+  rules:
+    - host: grafana.nav.ovh
+      http:
+        paths:
+          - path: /
+            pathType: Prefix
+            backend:
+              service:
+                name: grafana
+                port: {number: 3000}
+---
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: sonarqube
+  namespace: monitoring
+spec:
+  ingressClassName: traefik
+  rules:
+    - host: sonar.nav.ovh
+      http:
+        paths:
+          - path: /
+            pathType: Prefix
+            backend:
+              service:
+                name: sonarqube
+                port: {number: 9000}
+---
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: prometheus
+  namespace: monitoring
+spec:
+  ingressClassName: traefik
+  rules:
+    - host: prom.nav.ovh
+      http:
+        paths:
+          - path: /
+            pathType: Prefix
+            backend:
+              service:
+                name: prometheus
+                port: {number: 9090}