fix: 结果区更新时保留「复制」按钮

[cursor]

Bug and impact

Multiple tools write output with element.textContent = ... on the shared .result-box container that also holds the per-box 复制 button. In the DOM, assigning textContent on a parent replaces all descendants with a single text node, so the copy control disappeared after the first successful operation (JSON 格式化、Base64、时间戳、Hash、UUID 等). Users lost one-click copy for the rest of the session unless they reloaded the page.

Root cause

textContent on the parent result-box clears child nodes, including the <button class="copy-btn">.

Fix

• Wrap placeholder output in <span class="result-text"> in each affected panel.
• Add setResultBoxText(boxId, text) to update only that span.
• Point copyResult at .result-text when present.

Validation

• Parsed the inline <script> with new Function(...) under Node to confirm syntax.
• Manual expectation: run any tool that fills a result box; the 复制 button remains visible and still copies the result text.

No automated test harness exists in this static single-file repo.