fix(dev): use current Node runtime in worktrees

[boybook]

Summary

• pass the Node executable running dev-runtime.js to Electron through TX5DR_DEV_NODE_PATH
• allow Turbo to forward the development-only environment variable
• use the override only in the unpackaged development runtime

Context

Source worktrees do not necessarily contain resources/bin/<triplet>/node because packaged runtime binaries are ignored build resources. dev:electron previously tried to launch that missing packaged path and failed with ENOENT even though the development process already had a working Node executable.

The startup script now defaults the override to process.execPath, while still allowing an explicit caller-provided path. Packaged and production runtimes continue to resolve Node from application resources.

Validation

• yarn workspace @tx5dr/electron-main build
• yarn workspace @tx5dr/electron-main lint
• yarn workspace @tx5dr/electron-main test (10 files, 45 tests)
• node --check scripts/dev-runtime.js
• Turbo JSON parse check
• git diff --check