feat(v2/nav): add networking cluster + DevSecOps to quick-nav

Grows the quick-nav bar to 25 destinations:
  - New networking cluster (after cloud): 🌐 Networking · 🕸️ Istio · 🔗 K8s Net
  - DevSecOps joins the security cluster: 🔐 Security · 🛡️ DevSecOps

Short labels as usual (K8s Net for Kubernetes Networking). Template-only change
to docs/overrides/main.html; reuses the existing .nb-quicknav pill styling, no
CSS change, no page regeneration, V2-only. All target pages verified and
mkdocs build -f v2-mkdocs.yml passes with all 25 links rendering.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/overrides/main.html

@@ -14,7 +14,8 @@
   (even when the underlying page title is long):
     discovery (Topic Map · Digest · Videos) → platform (Kubernetes · Docker)
     → delivery (GitOps · CI/CD) → IaC (Terraform · Ansible)
-    → cloud (AWS · Azure · GCP) → security → ops (Observability · SRE · DevOps)
+    → cloud (AWS · Azure · GCP) → networking (Networking · Istio · K8s Net)
+    → security (Security · DevSecOps) → ops (Observability · SRE · DevOps)
     → data (Messaging) → AI/ML (AI & MCP · MLOps) → Methodology,
   with V1 Archive muted last.
 -#}
@@ -33,7 +34,11 @@
     <a class="nb-quicknav__link" href="/aws/">☁️ AWS</a>
     <a class="nb-quicknav__link" href="/azure/">☁️ Azure</a>
     <a class="nb-quicknav__link" href="/GoogleCloudPlatform/">☁️ GCP</a>
+    <a class="nb-quicknav__link" href="/networking/">🌐 Networking</a>
+    <a class="nb-quicknav__link" href="/istio/">🕸️ Istio</a>
+    <a class="nb-quicknav__link" href="/kubernetes-networking/">🔗 K8s Net</a>
     <a class="nb-quicknav__link" href="/kubernetes-security/">🔐 Security</a>
+    <a class="nb-quicknav__link" href="/devsecops/">🛡️ DevSecOps</a>
     <a class="nb-quicknav__link" href="/monitoring/">📈 Observability</a>
     <a class="nb-quicknav__link" href="/sre/">🛠️ SRE</a>
     <a class="nb-quicknav__link" href="/devops/">♾️ DevOps</a>