docs: add CLAUDE.md for Claude Code integration

.gitignore

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+.claude
 coverage.*

CLAUDE.md

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+# storage
+
+Shared Go library for AWS S3 storage operations.
+
+## Shared Documentation
+
+@../docs/claude/architecture.md
+@../docs/claude/go-services.md
+@../docs/claude/conventions.md
+
+## Library Information
+
+### Purpose
+
+Provides standardized S3 object storage utilities with presigned URL generation. Used by services that need to store and serve files (PDFs, images, etc.).
+
+### Usage
+
+```go
+import "gitlab.com/unboundsoftware/shiny/storage"
+
+// Create storage with automatic AWS config
+s3Storage, err := storage.New("my-bucket")
+
+// Upload and get presigned URL (15-minute expiration)
+url, err := s3Storage.Store("path/to/file.pdf", reader, "application/pdf")
+```
+
+### Features
+
+- **Managed uploads** - For large files with multipart upload
+- **Direct uploads** - For smaller files or custom config
+- **Presigned URLs** - 15-minute expiration for secure access
+- **Configurable part size** - For multipart upload optimization
+
+### Configuration
+
+Uses AWS SDK v2, loading config from:
+- Environment variables (`AWS_REGION`, `AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY`)
+- Shared config files (`~/.aws/config`, `~/.aws/credentials`)
+- IAM roles (on AWS infrastructure)