Module dotenv/edit/editDotenvFile

FS-level dotenv editor adapter (target resolution + template bootstrap).

Requirements addressed:

• Deterministic target selection across getdotenv paths only.
• Scope axis (global|env) × privacy axis (public|private).
• Template bootstrap: copy <target>.<templateExtension> to <target> when needed.
• Edit in place while preserving formatting via the pure text editor.