[ci skip] k8s portal: fix setup script + add onboarding hub (5 new pages)

Bug fixes:
- CA cert now populated in ConfigMap (was empty → TLS failures)
- Remove useless heredoc quote escaping in setup script
- Fix homepage: VPN callout, correct verification command (get namespaces)
- Fix false-positive sensitive=true on ingress_path, tls_secret_name,
  truenas_host, ollama_host, client_certificate_secret_name

New pages (direct Svelte, no mdsvex dependency):
- /onboarding: step-by-step guide (VPN, kubectl, git, first PR)
- /architecture: cluster topology, storage, networking, tiers
- /services: catalog of 70+ services with URLs
- /contributing: PR workflow, what you can/can't change, NEVER list
- /troubleshooting: common issues and fixes

Navigation bar added to layout. All pages use consistent docs styling.

Requires Docker image rebuild: cd stacks/platform/modules/k8s-portal/files
&& docker build -t viktorbarzin/k8s-portal:latest . && docker push

stacks/platform/modules/k8s-portal/main.tf

@@ -1,5 +1,9 @@
 variable "tls_secret_name" {}
 variable "tier" { type = string }
+variable "k8s_ca_cert" {
+  type    = string
+  default = ""
+}
 
 resource "kubernetes_namespace" "k8s_portal" {
   metadata {
@@ -23,8 +27,7 @@ resource "kubernetes_config_map" "k8s_portal_config" {
   }
 
   data = {
-    # CA cert extracted from kubeconfig — will be populated with cluster CA cert
-    "ca.crt" = ""
+    "ca.crt" = var.k8s_ca_cert
   }
 }