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>

routers/web/org/mention.go

@@ -0,0 +1,42 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package org
+
+import (
+	"net/http"
+
+	"code.gitea.io/gitea/models/organization"
+	"code.gitea.io/gitea/modules/util"
+	shared_mention "code.gitea.io/gitea/routers/web/shared/mention"
+	"code.gitea.io/gitea/services/context"
+)
+
+// GetMentionsInOwner returns JSON data for mention autocomplete on owner-level pages.
+func GetMentionsInOwner(ctx *context.Context) {
+	// for individual users, we don't have a concept of "mentionable" users or teams, so just return an empty list
+	if !ctx.ContextUser.IsOrganization() {
+		ctx.JSON(http.StatusOK, []shared_mention.Mention{})
+		return
+	}
+
+	// for org, return members and teams
+	c := shared_mention.NewCollector()
+	org := organization.OrgFromUser(ctx.ContextUser)
+
+	// Get org members
+	members, _, err := org.GetMembers(ctx, ctx.Doer)
+	if err != nil {
+		ctx.ServerError("GetMembers", err)
+		return
+	}
+	c.AddUsers(ctx, members)
+
+	// Get mentionable teams
+	if err := c.AddMentionableTeams(ctx, ctx.Doer, ctx.ContextUser); err != nil {
+		ctx.ServerError("AddMentionableTeams", err)
+		return
+	}
+
+	ctx.JSON(http.StatusOK, util.SliceNilAsEmpty(c.Result))
+}