feat: add S3-compatible storage interface (Layer 1)

[mudigal]

Summary

• Add S3-compatible storage interface that provides familiar S3 API semantics on top of Layer 0 blob storage
• S3 pallet internally creates Layer 0 buckets, encapsulating the storage layer from clients
• Clients only interact with the S3 layer while Layer 0 provides underlying storage guarantees (checkpoints, challenges, slashing)

Components Added

Component	Description
s3-primitives	Core types (ObjectMetadata, S3BucketInfo) and validation functions
pallet-s3-registry	On-chain S3 bucket/object metadata with automatic Layer 0 bucket creation
s3-client	High-level SDK using subxt 0.44 for chain operations

Key Features

• Bucket operations: create, delete, head, list
• Object operations: put, get, delete, copy, list with prefix/delimiter support
• S3 naming rules validation (3-63 chars, lowercase alphanumeric + hyphens)
• Content-addressed storage via CID (blake2-256)
• User-defined metadata support

Architecture

┌─────────────────────────────────────────────────────────────┐
│                    S3 Client SDK                            │
│    (put_object, get_object, list_objects, etc.)             │
└─────────────────────────────────────────────────────────────┘
        │                                      │
        ▼                                      ▼
┌───────────────────────┐    ┌─────────────────────────────────┐
│   pallet-s3-registry  │    │   Provider Node (Layer 0)       │
│   (On-chain metadata) │    │   (Unchanged - blob storage)    │
└───────────────────────┘    └─────────────────────────────────┘

Test plan

• cargo test -p s3-primitives - 3 tests pass
• cargo test -p pallet-s3-registry - 10 tests pass
• cargo test -p s3-client - 1 test passes
• Integration test with running infrastructure (just s3-example)

🤖 Generated with Claude Code