Extend issue context popup beyond markdown content (#36908)

Extend the issue context popup beyond markdown. Any link rendered with
the `ref-issue` class now gets the popup, which covers commit titles and
issue titles everywhere they appear (repo home, commits list, blame,
branches, graph, PR commits, issue/PR pages, compare, …). For surfaces
that synthesize links without markdown autolinking (dashboard activity
feed, pulse page, commit merged-PR line), opt in by adding
`data-ref-issue-container` on a parent (or `ref-issue` on the link).

- Use `html_url` from the backend payload instead of synthesizing links
client-side
- Fetch outside the component, stateless, with a per-URL cache
- Small hover delay so passing over a link doesn't fire a request
- Drop the loading state (shifted layout)
- Make both links in the tooltip work; prevent nested tooltips
- Fix feed title `<a>` width so the tooltip only shows on link hover

Co-authored-by: Claude (Opus 4.6) <noreply@anthropic.com>

web_src/js/markup/content.ts

@@ -5,7 +5,6 @@ import {initMarkupRenderAsciicast} from './asciicast.ts';
 import {initMarkupTasklist} from './tasklist.ts';
 import {registerGlobalInitFunc, registerGlobalSelectorFunc} from '../modules/observer.ts';
 import {initExternalRenderIframe} from './render-iframe.ts';
-import {initMarkupRefIssue} from './refissue.ts';
 import {toggleElemClass} from '../utils/dom.ts';
 
 // code that runs for all markup content
@@ -26,6 +25,5 @@ export function initMarkupContent(): void {
     initMarkupCodeMermaid(el);
     initMarkupCodeMath(el);
     initMarkupRenderAsciicast(el);
-    initMarkupRefIssue(el);
   });
 }