Add `crossplane resource simulate`

[haarchri]

What

Add crossplane resource simulate as an alpha command, per the accepted design (crossplane/cli#181,design/one-pager-cli-simulate.md): given YAML for one or more MRs (-f), show what applying them would do.

• For each input resource, fetch the live MR from the cluster if one exists.
• Diff desired against live spec client-side; this is the [?] approximate path from the design, and until the plan layer exists every resource takes it, marked accordingly.
• A resource with no live counterpart plans as a create.
• Summary line and -o plan|diff|json|yaml, shared with project simulate

Acceptance criteria

• crossplane resource simulate -f resources.yaml (alpha) previews creates and updates against the current kubeconfig context.
• Output marks all results as approximate ([?]) until the plan layer exists, with the documented closing warning.
• Output formats and summary shared with project simulate (no second implementation).

Out of scope

• Plan servers and provider-computed diffs, --all provider upgrade preview, --provider-images (follow-up issue: plan layer).

Dependencies

Depends on the work in #367