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

skills/similarity-search-patterns/SKILL.md

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+---
+name: similarity-search-patterns
+description: Implement efficient similarity search with vector databases. Use when building semantic search, implementing nearest neighbor queries, or optimizing retrieval performance.
+---
+
+# Similarity Search Patterns
+
+Patterns for implementing efficient similarity search in production systems.
+
+## Use this skill when
+
+- Building semantic search systems
+- Implementing RAG retrieval
+- Creating recommendation engines
+- Optimizing search latency
+- Scaling to millions of vectors
+- Combining semantic and keyword search
+
+## Do not use this skill when
+
+- The task is unrelated to similarity search patterns
+- 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.