docs: Add copy button to prompt blocks via sphinx-copybutton

Target p:last-child inside prompt admonitions so the button lands
inside the div (same positioning context as code blocks). Hidden
at rest, visible on hover — identical behavior to code blocks.

- copybutton_selector extended with div.admonition.prompt > p:last-child
- copybutton_exclude adds .admonition-title
- Hover CSS for button visibility inside prompt blocks
- Fix hidden title still taking space (display:none suffices)
- Remove bottom margin on last paragraph to tighten padding

Author: tony

docs/_static/css/custom.css

@@ -228,6 +228,23 @@ div.admonition.prompt > p {
   color: var(--color-foreground-primary);
 }
 
+div.admonition.prompt > p:last-of-type {
+  margin-bottom: 0;
+}
+
+/* Copy button — inserted afterend of p:last-child, so it
+ * lands inside the prompt div. position:relative on the
+ * prompt div provides the positioning context. */
+div.admonition.prompt > button.copybtn {
+  background: transparent !important;
+  border: none !important;
+}
+
+div.admonition.prompt:hover > button.copybtn,
+div.admonition.prompt > button.copybtn.success {
+  opacity: 1;
+}
+
 div.admonition.prompt > p:last-child {
   margin-bottom: 0;
 }

docs/conf.py

@@ -138,6 +138,8 @@
 copybutton_prompt_is_regexp = True
 copybutton_remove_prompts = True
 copybutton_line_continuation_character = "\\"
+copybutton_selector = "div.highlight pre, div.admonition.prompt > p:last-child"
+copybutton_exclude = ".linenos, .admonition-title"
 
 # sphinxext-rediraffe
 rediraffe_redirects = "redirects.txt"