chore: release v4.0.0 - sync 550+ skills and restructure docs

skills/solidity-security/SKILL.md

@@ -0,0 +1,34 @@
+---
+name: solidity-security
+description: Master smart contract security best practices to prevent common vulnerabilities and implement secure Solidity patterns. Use when writing smart contracts, auditing existing contracts, or implementing security measures for blockchain applications.
+---
+
+# Solidity Security
+
+Master smart contract security best practices, vulnerability prevention, and secure Solidity development patterns.
+
+## Use this skill when
+
+- Writing secure smart contracts
+- Auditing existing contracts for vulnerabilities
+- Implementing secure DeFi protocols
+- Preventing reentrancy, overflow, and access control issues
+- Optimizing gas usage while maintaining security
+- Preparing contracts for professional audits
+- Understanding common attack vectors
+
+## Do not use this skill when
+
+- The task is unrelated to solidity security
+- You need a different domain or tool outside this scope
+
+## Instructions
+
+- Clarify goals, constraints, and required inputs.
+- Apply relevant best practices and validate outcomes.
+- Provide actionable steps and verification.
+- If detailed examples are required, open `resources/implementation-playbook.md`.
+
+## Resources
+
+- `resources/implementation-playbook.md` for detailed patterns and examples.