feat: add solana-cu-minimalism skill — CU-efficiency checklist for Anchor/Pinocchio

[zheke01]

Summary

• Adds the solana-cu-minimalism skill: a compute-unit minimalism checklist applied while writing/reviewing Anchor or Pinocchio instruction handlers (redundant-constraint removal, zero-copy vs. heap allocation, CPI batching, hot-path logging)
• Net-new relative to the kit's existing security/QA tooling — pairs with the kit's existing /profile-cu and /benchmark commands rather than duplicating them; no entry in skill-registry.json currently covers CU-level code minimalism
• Includes references/cpi-and-account-patterns.md and references/compute-budget-basics.md for deeper guidance, loaded only as needed (progressive disclosure)

Validation

• SKILL.md passes the official skill checklist (kebab-case name, exact SKILL.md filename, no README inside the folder, description under 1024 chars with explicit WHAT + WHEN + negative triggers, no angle brackets in frontmatter)
• Manual triggering test against 16 realistic should-trigger/should-not-trigger prompts; found and fixed two overtrigger near-misses (conceptual CPI questions, security-only audits) by tightening the description
• Not yet run through the full with-skill/baseline subagent eval loop (skill-creator) — open to running that if reviewers want it