docs: improve coding pattern discoverability for coding agents

[LNSD]

Restructure the coding guidelines from .patterns/ into docs/code/ as discoverable markdown documents with YAML frontmatter, reducing context overhead for coding agents.

• Relocate pattern docs from .patterns/ to docs/code/ with simplified names
• Split idiomatic-rust.md into rust-modules.md, rust-type-design.md, and code-pattern-docs.md
• Add /code-pattern-discovery skill for loading relevant coding patterns
• Add /code-pattern-fmt-check skill for validating pattern doc formatting
• Convert /code-review command to a skill with pattern violation checks
• Update AGENTS.md to reference new skills and integrate patterns into the workflow

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Note

Reorganizes coding standards into discoverable pattern docs and introduces skills-based workflows for agents and CI.

• Moves pattern docs from .patterns/ to docs/code/ with YAML frontmatter and adds the spec code-pattern-docs.md
• Splits and expands patterns: rust-modules, rust-type-design, rust-error-handling, error-reporting, logging, documentation, testing-patterns, services-pattern, cargo-workspace-patterns, plus crate-specific docs (admin-api-*, metadata-db-*, udf-documentation)
• Adds skills: /code-pattern-discovery and /code-pattern-fmt-check; converts code review into /code-review skill with pattern checks
• Updates AGENTS.md and feature skills to reference new patterns; removes legacy .patterns/ and deprecated cmd
• Updates GitHub Action claude-code-review.yml to use the new /code-review skill and clearer instructions

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