feat: support operation capability

# Feature Request

## What problem are you facing?

function-shell cannot be used in `WatchOperation` or `Operation` pipelines (ops.crossplane.io/v1alpha1). When Crossplane attempts to run a pipeline step that references function-shell, it fails with:

`function capability check failed: function "function-shell" (active revision "function-shell-...") is missing required capabilities: operation`

## How could this Function help solve your problem?

`WatchOperation` is the intended Crossplane v2 mechanism for Day Two Operations — reacting to resource lifecycle events (creation, update, deletion) with side-effecting logic.

## Additional context

- function-python (crossplane-contrib/function-python) already supports operation capability as a reference implementation