feat(skill): add context: fork + agent to 4 analysis skills

packages/rules/.ai-rules/skills/code-explanation/SKILL.md

@@ -1,6 +1,8 @@
 ---
 name: code-explanation
 description: Use when explaining complex code to new team members, conducting code reviews, onboarding, or understanding unfamiliar codebases. Provides structured analysis from high-level overview to implementation details.
+context: fork
+agent: Explore
 ---
 
 # Code Explanation

packages/rules/.ai-rules/skills/performance-optimization/SKILL.md

@@ -1,6 +1,8 @@
 ---
 name: performance-optimization
 description: Use when optimizing code performance, addressing slowness complaints, or measuring application speed improvements
+context: fork
+agent: general-purpose
 ---
 
 # Performance Optimization

packages/rules/.ai-rules/skills/pr-review/SKILL.md

@@ -1,6 +1,8 @@
 ---
 name: pr-review
 description: Use when conducting manual PR reviews - provides structured checklist covering security, performance, maintainability, and code quality dimensions with anti-sycophancy principles
+context: fork
+agent: Explore
 ---
 
 # PR Review

packages/rules/.ai-rules/skills/security-audit/SKILL.md

@@ -1,6 +1,8 @@
 ---
 name: security-audit
 description: Use when reviewing code for security vulnerabilities, before shipping features, or conducting security assessments. Covers OWASP Top 10, secrets exposure, authentication, and authorization flaws.
+context: fork
+agent: general-purpose
 ---
 
 # Security Audit