feat: Add basic project structure and initial crates

- Added basic project structure with workspace and crates:
  `kvstore`, `vault`, `evm_client`, `cli_app`, `web_app`.
- Created initial `Cargo.toml` files for each crate.
- Added placeholder implementations for key components.
- Included initial documentation files (`README.md`, architecture
  docs, repo structure).
- Included initial implementaion for kvstore crate(async API, backend abstraction, separation of concerns, WASM/native support, testability)
- Included native and browser tests for the kvstore crate

README.md

@@ -0,0 +1,57 @@
+# Modular Rust System: Key-Value Store, Vault, and EVM Client
+
+This repository implements a modular, async, and cross-platform cryptographic stack in Rust. It is designed for use in both native (desktop/server) and WASM (browser) environments, supporting secure storage, cryptographic operations, and EVM (Ethereum) client functionality.
+
+## Crate Overview
+
+- **kvstore/**: Async key-value store trait and implementations (native: `sled`, WASM: IndexedDB).
+- **vault/**: Cryptographic vault for managing encrypted keyspaces and key operations. Uses `kvstore` for persistence.
+- **evm_client/**: EVM RPC client, integrates with `vault` for signing and secure key management.
+- **cli_app/**: (Planned) Command-line interface for scripting and automation.
+- **web_app/**: (Planned) WASM web app exposing the same APIs to JavaScript or browser scripting.
+
+## Architecture Highlights
+- **Async everywhere:** All APIs are async and runtime-agnostic.
+- **Conditional backends:** Uses Cargo features and `cfg` to select the appropriate backend for each environment.
+- **Secure by design:** Vault encrypts all key material at rest and leverages modern cryptography.
+- **Tested natively and in browser:** WASM and native backends are both covered by tests.
+
+## Building and Testing
+
+### Prerequisites
+- Rust (latest stable recommended)
+- For WASM: `wasm-pack`, Firefox or Chrome (for browser tests)
+
+### Native
+```sh
+cargo check --workspace --features kvstore/native
+```
+
+### WASM (kvstore only)
+```sh
+cd kvstore
+wasm-pack test --headless --firefox --features web
+```
+
+## Directory Structure
+```
+.
+├── kvstore/      # Key-value store trait and backends
+├── vault/        # Cryptographic vault
+├── evm_client/   # EVM RPC client
+├── cli_app/      # CLI (planned)
+├── web_app/      # Web app (planned)
+├── docs/         # Architecture docs
+└── README.md
+```
+
+## Roadmap
+- [x] Unified async trait for key-value storage
+- [x] Native and WASM backends for kvstore
+- [x] Cryptographic vault with password-protected keyspace
+- [x] EVM client with vault integration
+- [ ] CLI and web app targets
+- [ ] Full end-to-end integration
+
+## License
+MIT OR Apache-2.0