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/helmrelease.yaml

@@ -32,7 +32,15 @@ spec:
   chart:
     spec:
       chart: headlamp
-      version: ">=0.40.0 <0.41.0"   # Renovate maintains; chart appVersion pins the Headlamp image
+      # 0.41.x, NOT 0.40.x. Chart 0.40.1 shipped the `-session-ttl=86400` container arg BEFORE the
+      # backend flag existed: its image (appVersion v0.40.1) has no `session-ttl` flag, so the pod
+      # crashlooped with `flag provided but not defined: -session-ttl` (upstream issue #4883). The
+      # backend gained `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 (-session-ttl + the -oidc-* args from the externalSecret; useCookie stays default-false
+      # so `-oidc-use-cookie` is NOT emitted) is supported by the v0.41.0 backend. Renovate maintains
+      # within 0.41.x; the appVersion continues to pin the Headlamp image.
+      version: ">=0.41.0 <0.42.0"
       sourceRef:
         kind: HelmRepository
         name: headlamp