fix: resolve bundled CLI node path

[codedogQBY]

Summary

• resolve Node.js from explicit env vars, PATH, and common desktop install locations before running the bundled ReadAny CLI
• return structured CLI failures with clearer Node-missing diagnostics instead of surfacing an unknown invoke error
• update bundled CLI resolver tests for absolute Node paths and missing-Node messaging

Tests

• cargo test --manifest-path packages/app/src-tauri/Cargo.toml readany_cli