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

docs/RepoStructure.md

@@ -0,0 +1,131 @@
+# SAL Repository Structure
+
+## Introduction
+
+This document describes the recommended structure for the SAL repository, reflecting the new modular architecture. The goal is to enable robust, maintainable, and WASM-compatible development, while supporting a CLI binary and Rhai scripting.
+
+---
+
+## Recommended Directory Layout
+
+```
+sal/
+├── arch/
+│   ├── Architecture.md
+│   └── RepoStructure.md   # ← this file
+├── Cargo.toml             # Workspace manifest
+├── kvstore/
+│   ├── Cargo.toml
+│   └── src/
+├── vault/
+│   ├── Cargo.toml
+│   └── src/
+├── evm_client/
+│   ├── Cargo.toml
+│   └── src/
+├── cli_app/
+│   ├── Cargo.toml
+│   └── src/
+│       ├── main.rs        # CLI binary entry point
+│       └── commands.rs
+├── web_app/
+│   ├── Cargo.toml
+│   └── src/
+├── rhai/
+│   └── src/
+│       └── lib.rs         # Rhai bindings and script API
+└── README.md
+```
+
+- **Each core component (`kvstore`, `vault`, `evm_client`, `rhai`) is a separate crate at the repo root.**
+- **CLI binary** is in `cli_app` and depends on the core crates.
+- **WebAssembly target** is in `web_app`.
+- **Rhai bindings** live in their own crate (`rhai/`), so both CLI and WASM can depend on them.
+
+---
+
+## Sample Workspace `Cargo.toml`
+
+```toml
+[workspace]
+members = [
+    "kvstore",
+    "vault",
+    "evm_client",
+    "cli_app",
+    "web_app",
+    "rhai",
+]
+```
+
+---
+
+## Component Details
+
+### kvstore
+- Async trait for key-value storage.
+- Native and WASM backends selected by features or `cfg`.
+
+### vault
+- Manages encrypted keyspaces and cryptographic operations.
+- Uses `kvstore` for persistence.
+
+### evm_client
+- Handles EVM RPC, uses `vault` for signing.
+
+### cli_app (Binary)
+- Provides CLI interface using `vault`, `evm_client`, and `rhai`.
+- Entry point: `cli_app/src/main.rs`.
+
+### web_app (WASM)
+- Exposes Rust APIs to JS using `wasm-bindgen`.
+- Depends on `vault`, `evm_client`, and `rhai`.
+
+### rhai
+- Contains all Rhai script bindings and API glue.
+- Shared by both CLI and WASM targets.
+
+---
+
+## Integration & Migration Notes
+
+- Move code from `src/hero_vault` and related modules into the new crates.
+- The CLI binary is now in `cli_app/src/main.rs`, depending on all core crates.
+- Rhai bindings are centralized in the `rhai/` crate, making them reusable.
+- If you need to keep a legacy `src/` for migration, do so temporarily—plan to remove it once the transition is complete.
+
+---
+
+## Rationale
+
+- **Idiomatic Rust**: Each crate at the root, easy to manage, test, and publish.
+- **Maintainability**: Clear separation of concerns, easy to extend.
+- **WASM & CLI**: Both targets are first-class, sharing as much code as possible.
+- **Rhai Integration**: Centralized, reusable scripting interface.
+
+---
+
+## Example: How to Build the CLI Binary
+
+```sh
+cd cli_app
+cargo build --release
+cargo run -- <args>
+```
+
+The CLI binary will be compiled as `target/release/cli_app`.
+
+---
+
+## Example: How to Build the WASM Target
+
+```sh
+cd web_app
+wasm-pack build --target web
+```
+
+---
+
+## Summary
+
+This structure enables modular, scalable development for both CLI and browser targets, with robust support for async, WASM, and scripting via Rhai.