brand,mermaid - support font family and weight forwarding

[cscheid]

Minimal example:

_brand.yml

color:
  palette:
    red: "#FFB080"
  primary: red
  foreground: green
  background: black
typography:
  fonts:
    - family: "Ubuntu"
      source: google
      weight: [400, 700]
  base:
    family: "Ubuntu"
    weight: 700

test.qmd

---
format: html
---

## Hello, world

[A link](https://quarto.org).

```{mermaid}
flowchart LR
  A[Hard edge] --> B(Round edge)
  B --> C{Decision}
```

Output