Add WebAssembly wrapper for the core reVault API

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Goal

Provide a WebAssembly wrapper around the core reVault API so browser and JavaScript/TypeScript clients can use the core lockbox functionality without going through the CLI.

Context

The Rust crate currently appears to be lockbox_core; confirm whether the public package/API should be named revault_core, lockbox_core, or a dedicated WASM package name before publishing.

The wrapper should target WASM consumers while keeping the core Rust API as the source of truth.

Proposed scope

• Add a WASM-friendly wrapper crate or package for the core API.
• Use wasm-bindgen or the project-preferred WASM binding approach.
• Expose ergonomic JavaScript/TypeScript bindings.
• Support the expected runtime targets, at minimum browser use, and document Node support if included.
• Wrap common lockbox operations needed by clients.
• Convert Rust errors into clean, stable JS-facing errors.
• Avoid exposing raw secrets longer than necessary and document WASM memory/security limitations.
• Add examples for browser and TypeScript usage.

Testing

• Add CI coverage that builds the WASM target.
• Add smoke tests for the exported bindings.
• Add API-level tests for representative create/open/read/write flows where practical.

Notes

The core crates already contain some wasm32-unknown-unknown dependency configuration, so this should start by auditing the existing WASM readiness before introducing new structure.