[Bug] Heading alignment "broken" when text spans multiple lines

### Before submitting

- [x] I am using the latest version of Quarkdown.
- [x] I am using Java 17 or later (`java -version`).

### Description

The paragraph numbering (rendered via ::before) is currently behaving as an inline element. When an heading contains a line break (`.br`) or wraps naturally, the second line starts below the number instead of remaining aligned with the first line of text.

### Input

```markdown
.doctype {paged}
.pageformat width:{10cm} height:{5cm} margin:{1cm}

# A multiline title
```

### Actual output

### Expected output

### Operating system

_No response_

### Additional context

_No response_

Reproduce the issue with the provided Quarkdown input, including a naturally wrapped heading or a line break via `.br`. Trace the heading rendering and `::before` paragraph-numbering behavior; done means every continuation line remains aligned with the first line of heading text.

Written by the indexing model from the issue text.