feat(k8s): data-declared generic Platform components (K4a)

[astrojerms]

K4(a) — Data-declared generic Platform components

Delivers the roadmap's intent that Platform is generic support (Terraform-provider style), not a curated grab-bag of preferred charts. Platform can now install any Helm chart with no code change.

Generic components map

kind: Platform
spec:
  kubeconfigPath: { $ref: {...} }
  # presets — default chart coords, enable with a flag:
  traefik: { enabled: true }
  longhorn: { enabled: true }
  # generic — install ANY chart, no code change:
  components:
    prometheus:
      chart: { repo: https://prometheus-community.github.io/helm-charts, name: kube-prometheus-stack, version: 65.0.0 }
      values: { grafana: { enabled: false } }

• The named fields (traefik/cloudflared/argocd/nvidiaDevicePlugin/nfsProvisioner/longhorn) are now explicitly presets — they only fill default chart coordinates on top of the generic path, not baked-in opinion.
• Generic component: enabled defaults true (listing it opts in; set false to disable without removing); namespace defaults to the release name; a generic entry sharing a preset's name overrides it.
• enabledComponents merges presets (declaration order) then generic (sorted by name) deterministically, via a shared buildComponentRelease helper. Get/Delete/prune/plan key on release name and work unchanged.
• #Platform.components? schema entry (chart.repo + chart.name required).

Fully back-compat: existing preset-only specs behave identically (all prior tests pass unchanged).

Remaining

K4(b) — deployment methods as providers (Kustomize/Flux as new kinds) — stays open; tracked in ROADMAP.

Tests

Generic install (chart/ns default-to-name/values thread-through), enabled:false + missing-chart-coords skip (defensive), generic-overrides-preset dedup, preset-then-generic ordering.

Local CI (k8s plugin module): build, go test ./..., gofmt, vet, staticcheck, golangci-lint (0 issues), modernize — all green.