Implement per-target .env handling in install.sh #5
Description
Goal
Add .env handling per install target (project/global): copy/merge/skip behavior during install.
Scope
- Define desired behavior (copy vs merge vs skip)
- Implement in install.sh without introducing platform incompatibilities
- Document prompts/flags and edge cases
Acceptance criteria
- Installer can optionally place/manage .env per target
- Behavior is predictable and documented
- No secrets are committed by default