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>

templates/base/head_script.tmpl

@@ -19,13 +19,13 @@ If you introduce mistakes in it, Gitea JavaScript code wouldn't run correctly.
 		sharedWorkerUri: '{{AssetURI "js/eventsource.sharedworker.js"}}',
 		{{/* this global i18n object should only contain general texts. for specialized texts, it should be provided inside the related modules by: (1) API response (2) HTML data-attribute (3) PageData */}}
 		i18n: {
-			copy_success: {{ctx.Locale.Tr "copy_success"}},
-			copy_error: {{ctx.Locale.Tr "copy_error"}},
 			error_occurred: {{ctx.Locale.Tr "error.occurred"}},
 			remove_label_str: {{ctx.Locale.Tr "remove_label_str"}},
 			modal_confirm: {{ctx.Locale.Tr "modal.confirm"}},
 			modal_cancel: {{ctx.Locale.Tr "modal.cancel"}},
 			more_items: {{ctx.Locale.Tr "more_items"}},
+			copy_success: {{ctx.Locale.Tr "copy_success"}},
+			copy_error: {{ctx.Locale.Tr "copy_error"}},
 		},
 	};
 	{{/* in case some pages don't render the pageData, we make sure it is an object to prevent null access */}}