fix(delete): remove snapshot only after local file deletion succeeds

[jamesjohnsdev]

A failed os.Remove on the issue file left the snapshot deleted,
disabling modified detection for that issue on subsequent syncs.

Closes #17

---

Summary by cubic

Fix delete behavior to only remove a synced issue’s snapshot after the local file is successfully deleted. Prevents lost modified detection if the local delete fails. Closes #17.

• Bug Fixes
  • Defer snapshot removal until after the local issue file is deleted; applies only to synced issues.
  • Added tests for local-only delete, synced delete success (snapshot removed), and delete failure (snapshot preserved).

^{Written for commit 849a1c9. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}