i18n(panel): migrate hardcoded panel strings to en-US and translate all locales

Surface ~400 hardcoded English labels, tooltips, placeholders, dt/divider
text, modal okText/cancelText, and Spin loading from the panel pages
(clients/groups/inbounds/nodes/settings/xray/sub/index) into
web/translation/en-US.json under existing pages.<page>.* namespaces, with
JSX swapped to t(...). Brand and protocol identifiers (TLS, MTU, SNI,
NordVPN, Cloudflare WARP, etc.) stay literal.

Sync all 12 non-English locales (ar-EG, es-ES, fa-IR, id-ID, ja-JP,
pt-BR, ru-RU, tr-TR, uk-UA, vi-VN, zh-CN, zh-TW) to match en-US's
structure and translate the 521 new key paths per locale. Every locale
file now has 1539 lines, mirroring en-US ordering.

Also remove a dead duplicate "info": "Info" key under pages.inbounds
that collided with the new pages.inbounds.info.* object.

Backend: bulk attach/detach errors in web/service/client.go now route
through logger.Warningf (so they appear under /panel/api/server/logs/)
instead of only living on the response payload.

frontend/src/pages/groups/GroupsPage.tsx

@@ -411,7 +411,7 @@ export default function GroupsPage() {
         <AppSidebar />
         <Layout className="content-shell">
           <Layout.Content id="content-layout" className="content-area">
-            <Spin spinning={!fetched} delay={200} description="Loading…" size="large">
+            <Spin spinning={!fetched} delay={200} description={t('loading')} size="large">
               {!fetched ? (
                 <div className="loading-spacer" />
               ) : (