Load mentionValues asynchronously (#36739)

Eliminate a few database queries on all issue and pull request pages by
moving mention autocomplete data to async JSON endpoints fetched
on-demand when the user types `@`.

See https://github.com/go-gitea/gitea/pull/36739#issuecomment-3963184858
for the full table of affected pages.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/utils/match.ts

@@ -1,6 +1,8 @@
 import emojis from '../../../assets/emoji.json' with {type: 'json'};
 import {GET} from '../modules/fetch.ts';
-import type {Issue} from '../types.ts';
+import {showErrorToast} from '../modules/toast.ts';
+import {parseIssuePageInfo} from '../utils.ts';
+import type {Issue, Mention} from '../types.ts';
 
 const maxMatches = 6;
 
@@ -29,13 +31,36 @@ export function matchEmoji(queryText: string): string[] {
   return sortAndReduce(results);
 }
 
-type MentionSuggestion = {value: string; name: string; fullname: string; avatar: string};
-export function matchMention(queryText: string): MentionSuggestion[] {
+let cachedMentionsPromise: Promise<Mention[]> | undefined;
+let cachedMentionsUrl: string;
+
+export function fetchMentions(mentionsUrl: string): Promise<Mention[]> {
+  if (cachedMentionsPromise && cachedMentionsUrl === mentionsUrl) {
+    return cachedMentionsPromise;
+  }
+  cachedMentionsUrl = mentionsUrl;
+  cachedMentionsPromise = (async () => {
+    try {
+      const issueIndex = parseIssuePageInfo().issueNumber;
+      const query = issueIndex ? `?issue_index=${issueIndex}` : '';
+      const res = await GET(`${mentionsUrl}${query}`);
+      if (!res.ok) throw new Error(res.statusText);
+      return await res.json() as Mention[];
+    } catch (e) {
+      showErrorToast(`Failed to load mentions: ${e}`);
+      return [];
+    }
+  })();
+  return cachedMentionsPromise;
+}
+
+export async function matchMention(mentionsUrl: string, queryText: string): Promise<Mention[]> {
+  const values = await fetchMentions(mentionsUrl);
   const query = queryText.toLowerCase();
 
   // results is a map of weights, lower is better
-  const results = new Map<MentionSuggestion, number>();
-  for (const obj of window.config.mentionValues) {
+  const results = new Map<Mention, number>();
+  for (const obj of values) {
     const index = obj.key.toLowerCase().indexOf(query);
     if (index === -1) continue;
     const existing = results.get(obj);