Use relative-time to render absolute dates (#36238)

`<relative-time>` can render absolute dates when passed
[`threshold="P0Y"`](https://github.com/github/relative-time-element#threshold-string-default-p30d)
and `prefix=""`, so remove the previously used `<absolute-date>` element
in its favor.

Devtest before:

<img width="324" height="210" alt="Screenshot 2025-12-23 at 20 22 44"
src="https://github.com/user-attachments/assets/cf78e0e7-f480-415f-98d5-09b25f9d5a8b"
/>

Devtest after:

<img width="274" height="184" alt="Screenshot 2025-12-23 at 20 22 49"
src="https://github.com/user-attachments/assets/5e7d25f6-eea1-4a8c-ba71-02b570804b95"
/>

Repo activity (rendering unchanged):

<img width="1023" height="67" alt="image"
src="https://github.com/user-attachments/assets/2c4fd6cb-14ab-43c6-ae4b-f86946b28288"
/>

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

webpack.config.ts

@@ -39,7 +39,6 @@ const webComponents = new Set([
   // our own, in web_src/js/webcomponents
   'overflow-menu',
   'origin-url',
-  'absolute-date',
   // from dependencies
   'markdown-toolbar',
   'relative-time',