docs: add coding guidelines for contributors

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build Commands
+- `make build` - Build application binary
+- `make install` - Install application
+- `make proto-gen` - Generate Protobuf files
+- `make mod-tidy` - Run go mod tidy
+
+## Test Commands
+- `make test` - Run unit tests
+- `make test-unit` - Run all unit tests 
+- `make test-race` - Run tests with race detection
+- For single test: `go test -v -run TestName ./path/to/package`
+
+## Lint Commands
+- `make lint` - Run golangci-lint and formatting checks
+- `make format` - Format code using gofumpt, misspell and gci
+
+## Code Style Guidelines
+- **Imports**: Group by standard library, third-party, then project-specific with blank lines
+- **Error Handling**: Use custom errors from `types/errors.go` with `sdkerrors.Register`
+- **Naming**: camelCase for variables, PascalCase for functions/exported types, prefix errors with `Err`
+- **Organization**: Follow Cosmos SDK module pattern (`x/{module}/`, `types/`, `keeper/`)
+- **Types**: Prefer explicit types over interface{}, use pointers for mutable state
+- **Documentation**: Document public APIs thoroughly with standard Go doc comments
+- **Formatting**: Run `make format` before committing
+
+This project follows standard Go conventions and Cosmos SDK patterns with clear organization and consistent error handling.