Save current story by pressing Ctrl/Cmd+S

**Branch/Commit:**

Main branch

**Describe the feature:**

Support saving the changes of the current story by pressing Ctrl+S or Cmd+S.

**Problem:**

It's not really a problem, but a common muscle memory to try to save changes with Ctrl+S while switching between code and points.

**I will abide by the [code of conduct](https://github.com/fastruby/points/blob/main/CODE_OF_CONDUCT.md)**