docs: add CLAUDE.md for Claude Code integration

.gitignore

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 .idea
+.claude
 /release

CLAUDE.md

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+# presenter
+
+Shared Go library for GraphQL error presentation with coded errors.
+
+## Shared Documentation
+
+@../docs/claude/architecture.md
+@../docs/claude/go-services.md
+@../docs/claude/graphql.md
+@../docs/claude/conventions.md
+
+## Library Information
+
+### Purpose
+
+Provides a standardized GraphQL error presenter that handles coded errors across all microservices. Converts internal error codes to GraphQL error extensions.
+
+### Usage
+
+```go
+import "gitlab.com/unboundsoftware/shiny/presenter"
+
+// Create error presenter with valid codes and entities
+errorPresenter := presenter.New(logger, validCodes, validEntities, internalErrorCode)
+
+// Use in gqlgen server config
+srv := handler.NewDefaultServer(generated.NewExecutableSchema(cfg))
+srv.SetErrorPresenter(errorPresenter)
+```
+
+### Key Types
+
+- `CodedError` - Error type with code, entity, and params
+- `Code` - Error code type
+- `Entity` - Error entity type
+
+### Error Extensions
+
+Errors are presented with extensions:
+- `code` - The error code (mapped to valid codes or internal error)
+- `errorEntity` - The entity related to the error (optional)
+- `params` - Additional error parameters (optional)