feat(web): add Discord link to sidebar account menu

Add a "Join our Discord" entry to the account dropdown's external-links
group, opening https://discord.gg/wdNEHETs87 in a new tab. lucide-react
has no Discord brand glyph, so include a small inline Discord SVG icon
(brand color). Add the joinDiscord label to all 8 locales.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/i18n/locales/zh-Hant.ts

@@ -36,6 +36,7 @@ const zhHant = {
     helpDocs: '輔助說明',
     featureRequest: '需求建議',
     starOnGitHub: '在 GitHub 上 Star',
+    joinDiscord: '加入 Discord 社群',
     create: '建立',
     edit: '編輯',
     delete: '刪除',