Expose registered mutations and firing-set; export golden serializer

[sourcehawk]

Towards #132

Description

Adds the read-only framework introspection surface and golden serializer export that the version-matrix golden generator (later sub-PRs) builds on. No reconcile-path behavior changes; every addition is an inert getter or a thin wrapper.

What changed

• New concepts.MutationInspector interface (pkg/component/concepts/mutation_inspector.go): RegisteredMutations() []string and FiringSet() ([]string, error).
• Implemented on generic.BaseResource: iterates its existing Mutations. A nil Feature fires unconditionally; otherwise Feature.Enabled() decides. RegisteredMutations dedupes in registration order; FiringSet preserves registration order and propagates gate errors wrapped with the mutation name.
• Implemented on *component.Component as the deduplicated union across managed (non read-only) resources, mirroring the Preview iteration. Read-only resources and resources that do not implement the interface contribute nothing; a managed resource's FiringSet error is wrapped with the resource identity and propagated.
• Delegation block plus a var _ concepts.MutationInspector = (*Resource)(nil) compile-time assertion on every primitive Resource (all 21 single-kind primitives and the 4 unstructured sub-resources: static, task, workload, integration). The assertion makes a missed primitive a build failure.
• Exported golden.Serialize(obj, scheme) and golden.SerializeComponent(objs, scheme) as thin wrappers over the existing private serializeObject. Refactored CompareComponentYAML to reuse SerializeComponent (DRY); output stays byte-identical.

New public surface

• concepts.MutationInspector interface { RegisteredMutations() []string; FiringSet() ([]string, error) }
• golden.Serialize(client.Object, *runtime.Scheme) ([]byte, error)
• golden.SerializeComponent([]client.Object, *runtime.Scheme) ([]byte, error)

Testing

• TDD throughout (failing test first, then minimal implementation) for BaseResource, Component, the statefulset anchor, and the golden serializer.
• BaseResource: dedup, nil-gate-fires, enabled/disabled gates, gate-error propagation.
• Component: union of registered mutations and firing-sets, read-only exclusion, error propagation.
• Primitives: statefulset satisfies the interface and reports its firing-set; the var _ assertions cover the remaining 24 resource types at compile time.
• Golden: Serialize is byte-identical to what CompareYAML writes; SerializeComponent joins multi-document YAML identically to CompareComponentYAML; existing golden tests still pass.
• make all is green (fmt, lint, test, test-examples, build-examples).