Skip call sign auto-detection inside code and pre elements

[Copilot]

searchCallsigns() was marking up call signs inside <code> and <pre> elements, which is nonsensical in code examples (e.g., the SM8AYA on the docs site's "Getting Started" snippet).

Added CODE and PRE to the TreeWalker's parent-tag skip list, alongside the already-skipped SCRIPT, STYLE, and CALL-SIGN:

if (!parent || parent.tagName === 'SCRIPT' || 
    parent.tagName === 'STYLE' || 
    parent.tagName === 'CALL-SIGN' ||
    parent.tagName === 'CODE' ||
    parent.tagName === 'PRE') {
  return NodeFilter.FILTER_REJECT;
}

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