Add eko init --from <snapshot-id> flag to bootstrap a project from a snapshot #111

🎯 Goal

Extend eko init with a --from <snapshot-id> flag that initializes a fresh .eko/ directory and immediately restores the specified snapshot into the current empty directory — useful for onboarding onto a shared project checkpoint.

💡 Expected Usage

mkdir new-project && cd new-project
eko init --from 8c9d1a2f
# Eko initialized.
# Restored snapshot 8c9d1a2f into current directory.

🛠️ Implementation Steps

1. Add --from string flag to cmd/init.go.
2. After standard eko init logic runs, if --from is set, call internal/snapshot.RestoreSnapshot() with the resolved snapshot path.
3. Print a combined success message.
4. Add unit tests in cmd/commands_test.go.

📖 See full details in GOOD_FIRST_ISSUES.md — Issue #17
🌟 Great for first-time contributors! Read CONTRIBUTING.md to get started.