feat: add copy button to action step header, improve other copy buttons (#37744)

- Adds a copy button to each action step header that copies the step's
rendered log output to clipboard.
- Extract a shared `copyToClipboard(target, content)` helper in
`clipboard.ts` that adds SVG success/failure feedback.
- `is-loading` height for the new helper is sourced from
`--loading-size`.
- Change actions log timestamp format to include seconds.

The indented-markdown code-block fix has moved to #37748.

<img width="244" height="165" alt="copystep"
src="https://github.com/user-attachments/assets/ce286b51-f77b-4d82-b161-ca0aa7ec4fdc"
/>

<img width="187" height="150" alt="copybt"
src="https://github.com/user-attachments/assets/5366b290-b776-496d-8dd4-58d5fa60be92"
/>

Fixes: https://github.com/go-gitea/gitea/issues/26116

---
This PR was written with the help of Claude Opus 4.7

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Nicolas <bircni@icloud.com>

web_src/css/modules/animations.css

@@ -13,6 +13,7 @@
 }
 
 .btn.is-loading > *,
+.btn-octicon.is-loading > *,
 .button.is-loading > * {
   opacity: 0;
 }
@@ -23,7 +24,7 @@
   display: block;
   left: 50%;
   top: 50%;
-  height: min(4em, 66.6%);
+  height: var(--loading-size, min(4em, 66.6%));
   width: fit-content; /* compat: safari - https://bugs.webkit.org/show_bug.cgi?id=267625 */
   aspect-ratio: 1;
   transform: translate(-50%, -50%);