feat(user): report on another user's time entries

- Add user_id parameter to fetch_issues_with_spent_time().
- Support numeric ID, login, or full name resolution.
- Reject ambiguous names and unknown users with clear messages.
- Add CLI flags: --user-id, --user-login, --user-name.
- Only allow one user flag at a time.
- Add ResourceNotFoundError handling.
- Update README with usage examples.
- Add tests for user resolution and CLI flags.

Closes #40

redmine_reporter/__init__.py

@@ -1 +1 @@
-__version__ = "1.6.1"
+__version__ = "1.7.0"