Task points (story points)

**Is your feature request related to a problem? Please describe.**
No. Just an incremental feature.

**Describe the solution you'd like**
Task points (story points).
- The user would give a value between [1, ..., 100]
```bash
tb --points @3 21
```

**Additional context**
- It would be nice and helpfull to measure my efforts with computed "story points" value.
- Externally, this value is based on an analysis of 'complexity X time_estimates'.
- In the future, it could have another feature based on calculating these points within a board or timeline.

The issue names no files, tests, or implementation entry points. Start by running the proposed `tb --points @3 21` example and tracing how the existing CLI handles task commands; clarify point storage, display, validation, and acceptance criteria before implementation.

Written by the indexing model from the issue text.