platform: move Headlamp out of the gating platform tier + fix -session-ttl crashloop

Headlamp's HelmRelease sat in the wait:true `platform` Flux tier. Its pod
crashlooped (`flag provided but not defined: -session-ttl` — chart 0.40.1
renders a container arg the appVersion v0.40.1 backend lacks; upstream
kubernetes-sigs/headlamp#4883), and because it gated `platform`, the whole
chain stalled: platform Ready=Unknown -> platform-config, oauth2-proxy,
apps-wave-0/1/2 and apps-vms all Ready=False "dependency not ready".

Part A (unblock + durable lesson): a leaf UI must never gate the chain. Move
all Headlamp resources into a new non-gating Flux Kustomization
clusters/base/headlamp.yaml (dependsOn platform-config, wait:false, SOPS
decryption patched per-env in clusters/dev) — mirroring oauth2-proxy exactly.
The new Kustomization owns the whole platform/headlamp component; its HTTPRoute
moves from platform-config into platform/headlamp/kustomization.yaml. Removed
headlamp from platform/kustomization.yaml and its httproute from
platform-config/kustomization.yaml. Now a crashlooping Headlamp can never stall
platform/platform-config/apps.

Part B (make it start): pin the chart to 0.41.0 (`>=0.41.0 <0.42.0`). The
backend added `f.Int("session-ttl", …)` in v0.41.0 and chart 0.41.0 pins that
same image (appVersion == chart version), so chart+image realign; every arg the
chart renders for our values is supported. OIDC config + per-user RBAC
(clusterRoleBinding.create:false) unchanged.

Gate: `make -C ci gate` PASS.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

platform/headlamp/kustomization.yaml

@@ -1,9 +1,14 @@
 ---
 # Headlamp — Kubernetes dashboard with Keycloak native-OIDC login + per-user RBAC (ADR-0014).
-# CONTROLLERS half: the HelmRepository + HelmRelease (chart installs the Deployment/Service/SA), the
-# SOPS-encrypted OIDC credential (decrypted by the `platform` Flux Kustomization), and the
-# default-deny + Cilium egress/ingress policies. The HTTPRoute is a Gateway API CR and lives in
-# platform-config (dependsOn platform) so the Gateway CRDs exist first — same split as grafana.
+# Rendered by its OWN post-platform Flux Kustomization (clusters/base/headlamp.yaml, dependsOn
+# platform-config, wait:false) — NOT by the gating `platform` tier, where a crashlooping UI
+# HelmRelease stalled the whole chain (DECISIONS-LOG "Headlamp gating stall"). This component owns
+# the HelmRepository + HelmRelease (chart installs the Deployment/Service/SA), the SOPS-encrypted
+# OIDC credential (decrypted per-env by the headlamp Kustomization), the default-deny + Cilium
+# policies, AND the HTTPRoute. The httproute (a Gateway API CR) now travels WITH the component here
+# rather than being referenced in-place from platform-config: the CRDs it needs
+# (gateway.networking.k8s.io) are registered by platform, and platform is Ready before this tier's
+# platform-config dependency completes, so ordering holds — same move oauth2-proxy already made.
 apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 namespace: headlamp
@@ -16,3 +21,4 @@ resources:
   - headlamp-oidc-credentials.sops.yaml
   # default-deny baseline + Cilium ingress(gateway)/egress(apiserver+Keycloak) allows.
   - networkpolicy.yaml
+  - httproute.yaml       # dashboard ingress (was referenced in-place by platform-config)