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

skills/openapi-spec-generation/SKILL.md

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+---
+name: openapi-spec-generation
+description: Generate and maintain OpenAPI 3.1 specifications from code, design-first specs, and validation patterns. Use when creating API documentation, generating SDKs, or ensuring API contract compliance.
+---
+
+# OpenAPI Spec Generation
+
+Comprehensive patterns for creating, maintaining, and validating OpenAPI 3.1 specifications for RESTful APIs.
+
+## Use this skill when
+
+- Creating API documentation from scratch
+- Generating OpenAPI specs from existing code
+- Designing API contracts (design-first approach)
+- Validating API implementations against specs
+- Generating client SDKs from specs
+- Setting up API documentation portals
+
+## Do not use this skill when
+
+- The task is unrelated to openapi spec generation
+- 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.