fix(docs): enable mermaid diagrams via pymdownx.superfences custom_fences

[jdwit]

Summary

`docs/livestreams.md` already had a flowchart-LR mermaid block but rendered it as a literal code block because the SuperFences custom-fence handler wasn't configured.

Material for MkDocs bundles Mermaid.js automatically when the fence is declared this way; no extra plugin or runtime dependency (reference).

```yaml

• pymdownx.superfences:
  custom_fences:
  - name: mermaid
  class: mermaid
  format: !!python/name:pymdownx.superfences.fence_code_format
  ```

Verified locally with `uv run mkdocs build --strict`: the livestreams page now emits `

` which the Material runtime upgrades into an interactive SVG diagram.

Versions confirmed against PyPI via context7:



package
current floor
latest




mkdocs
`>=1.6`
1.6.1


mkdocs-material
`>=9.5`
9.7.6


pymdown-extensions
`>=10.7`
10.21.3



All current floors already accept the latest minors; no pyproject.toml change needed.
Test plan

 `uv run mkdocs build --strict` clean
 grep'd `site/livestreams/index.html` for `
`
 manual visual check on the deployed site after merge