improve(motoko): add Caffeine migration note for --default-persistent-actors

[marc0olo]

Summary

• Adds a migration note to pitfall #1 (actor vs persistent actor) explaining that the Caffeine platform used a moc fork with --default-persistent-actors, making persistent optional and all variables implicitly stable
• Helps agents understand why Caffeine-migrated code produces M0220 errors on standard moc, and what to do about it (persistent actor + transient var)

Addresses #136 (F6).

[github-actions]

Skill Validation Report

Validating skill: /home/runner/work/icskills/icskills/skills/motoko

Structure

• Pass: SKILL.md found

Frontmatter

• Pass: name: "motoko" (valid)
• Pass: description: (456 chars)
• Pass: license: "Apache-2.0"
• Pass: compatibility: (37 chars)
• Pass: metadata: (2 entries)

Markdown

• Pass: no unclosed code fences found

Tokens

File	Tokens
SKILL.md body	3,089
Total	3,089

Content Analysis

Metric	Value
Word count	1,753
Code block ratio	0.57
Imperative ratio	0.10
Information density	0.34
Instruction specificity	0.88
Sections	14
List items	10
Code blocks	21

Contamination Analysis

Metric	Value
Contamination level	low
Contamination score	0.00
Primary language category	config
Scope breadth	2

Result: passed

Project Checks

✓ Project checks passed for 1 skills (0 warnings)

[marc0olo]

Eval results

Output eval — Caffeine migration M0220 errors

	With skill	Without skill
Explains --default-persistent-actors made persistent optional	✅	❌
Says to add persistent to every actor	✅	❌
Mentions transient var for reset-on-upgrade variables	✅	❌
Total	3/3	0/3

Trigger evals: 13/13 should-trigger ✅ | 10/10 should-not-trigger ✅