Digit-only tags \d{3,7} does not start timetracking

Hi,

I've got trouble using only digit tags.

The following command does not start time tracking

```shell
$ timew start 07:50 :adjust "foo" "bar" "1111"
Unrecognized date range: ' '.
```

Putting a character in front of it, fixes the issue

```shell

```shell
$ timew start 07:50 :adjust "foo" "bar" "b1111"
Unrecognized date range: ' '.
```

* The length of the number must be between two and eight digits.
* The position of the tag doesn't matter.

```shell
$ timew --version
1.9.1
```

Start by reproducing the digit-only tag case with timew 1.9.1, then compare it with the working b1111 case and check how the start command parses tags and date ranges. Done means a tag of two to eight digits, in any position, starts time tracking without the reported error, while existing tag behavior remains intact.

Written by the indexing model from the issue text.