fix(docs): add ARIA tab semantics to the ASM/SAT spec switcher

[dmchaledev]

Summary

docs/index.html renders two buttons that switch the embedded Redoc viewer between the ASM and SAT OpenAPI specs. They had no ARIA roles or selected-state semantics — a screen reader user tabbing to them would hear two unlabeled buttons with no indication they're a tab pair or which one is currently showing.

This adds the standard ARIA tab pattern:

• role="tablist" on a wrapper around the two buttons (display: contents so it doesn't affect the existing flex layout)
• role="tab" + aria-controls="redoc-container" on each button
• aria-selected toggled between "true"/"false" in the existing activate() handler, kept in sync with the .active CSS class it already manages
• role="tabpanel" + aria-live="polite" on the Redoc container, so switching specs is announced

No visual or behavioral change — purely additive markup/attributes.

Pre-flight duplicate check

• I searched open issues and open PRs for changes to the same file(s)/endpoint(s) and did not find an existing one already covering this change. (Existing open work — sat/openapi.yaml: several write endpoints are missing a requestBody schema #39, Pin third-party GitHub Actions to full-length commit SHAs (supply-chain hardening) #57, sat/openapi.yaml: no 429/rate-limit documentation anywhere (inconsistent with asm/openapi.yaml) #58, fix(asm): resolve invalid webhook payload schema (readOnly/requestBody conflict) #59 — is scoped to the OpenAPI specs and CI workflows, not docs/index.html accessibility.)

Related issues/PRs

None found.

Testing

• git diff reviewed — change is confined to docs/index.html markup and the activate() function.
• Served the page locally (with copies of asm/openapi.yaml/sat/openapi.yaml alongside it, matching what deploy-docs.yml produces) and drove it with Playwright/Chromium:
  • Initial state: #tab-asm has aria-selected="true", #tab-sat has aria-selected="false".
  • After clicking the SAT tab: selection flips correctly (asm=false, sat=true), role="tablist"/"tab"/"tabpanel" all present.
  • Screenshot confirms the nav bar layout is pixel-identical to before (the display: contents wrapper doesn't introduce any visual box).
• Redoc itself didn't load in the sandboxed test environment (CDN unreachable there), but that's unrelated to this change — the markup/JS under test loads and behaves correctly independent of Redoc's own rendering.

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