fix(kubernetes): block metrics-server install on Talos clusters

[hlts2]

Fixes #422

Problem

When adding a marketplace app to a Talos cluster, the CLI reports a successful install even though nothing is actually installed:

civo k8s apps add metrics-server -c talosmetrics01
The application was installed in the Kubernetes cluster talosmetrics01

The marketplace metrics-server is only enabled for k3s clusters (https://github.com/civo/kubernetes-marketplace/blob/master/metrics-server/manifest.yaml), so the user has no way to know the install silently did nothing.

Scope

Only metrics-server is blocked on Talos. Other marketplace apps install fine on Talos clusters, so blocking all apps (as explored in #593) would be too broad. On Talos, metrics-server must be installed separately (https://docs.siderolabs.com/kubernetes-guides/monitoring-and-observability/deploy-metrics-server).

Fix

• checkAppPlan now also returns the index of the resolved app, so validation runs against the canonical app name rather than raw user input. This closes the partial-match bypass (e.g. metrics resolves to metrics-server via strings.Contains).
• RequestedSplit exits early with a clear message when the resolved app is unsupported on the target cluster type.
• Added a unsupportedAppsByClusterType table with a TODO to remove it once cluster_type is surfaced through the API/civogo.

Tests

• Table-driven tests for isAppCompatibleWithClusterType.

Supersedes #593.

[hlts2]

Manual verification

Confirmed the behavior against real clusters.

Talos cluster — blocked with a clear error:

❯ ./cli kubernetes applications add metrics-server --cluster hiroto-talos
Error: metrics-server cannot be installed via the marketplace on talos clusters

k3s cluster — installs as before:

❯ ./cli kubernetes applications add metrics-server --cluster hiroto-k3s-1-36
The application was installed in the Kubernetes cluster hiroto-k3s-1-36

Talos cluster — other applications still install fine (no regression):

❯ ./cli kubernetes applications add loki --cluster hiroto-talos
The application was installed in the Kubernetes cluster hiroto-talos

Only metrics-server is blocked on Talos; all other marketplace apps are unaffected.