Click effect: button flashes green with "copied!" text and 1.15x
scale pulse, reverts after 1.2s. Failure case (clipboard API blocked
or HTTP context) shows red "failed" for 1.5s. Handler moved out of
inline onclick into a single delegated click listener at the doc
level so future copy buttons just need the .copy-btn class +
data-copy-text attribute.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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