Collapse platform build matrix behind a <details> group

[zackees]

Summary

docs/BOARD_STATUS.md renders the full per-platform CI badge matrix inline, which makes the page very long to scroll through before reaching anything else. Wrap the platform build matrix inside a <details> block so readers can expand it on demand rather than having it dominate the page by default.

Proposal

Wrap the "Per-platform CI badges" section (and/or each platform-family subsection) in GitHub-flavored <details> / <summary> so the matrix is collapsed by default:

<details>
<summary>Per-platform CI badges</summary>

### AVR
[![Build Arduino Uno](...)]
...

</details>

Options worth considering:

• One outer <details> around the entire matrix (simplest).
• A <details> per family (AVR, ESP32, Teensy, STM32, CH32V, ...) so readers can expand only the platform they care about.

Affected files

• docs/BOARD_STATUS.md — primary location of the matrix
• Any other doc that embeds the same badge list (search for actions/workflows/build- references)

Acceptance criteria

• Badge matrix is hidden behind a collapsible <details> group by default
• The page still renders correctly on github.com (markdown-inside-details works)
• Links to specific anchors (e.g. #esp32) still resolve if we go with per-family groups

[zackees]

Closing — prefer keeping the per-platform CI badge matrix expanded by default for at-a-glance visibility. The merged change in #94 was reverted in 53a077a.