Comparisons: Pulumi vs. Crossplane

[jkodroff]

Parent: #18673

Status: Revising existing page
Existing path: content/docs/iac/comparisons/crossplane.md

Revise the Pulumi vs. Crossplane comparison page following the structure defined in the parent epic #18673:

• Frontmatter: nav title = "Crossplane"; H1 = "Pulumi vs. Crossplane"
• "What is Pulumi?" shared shortcode
• "What is Crossplane?" neutral description
• Detailed comparison table (per the columns listed in Revise IaC -> Comparisons for IaC tools #18673)
• Key differences (sentences, per topic)
• Adoption: Coexistence, Conversion, and Import
• Next steps

Follow the tone/style rules in #18673: neutral, no marketing copy, no CTAs, no emojis, no video clips.