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/th-TH.ts

@@ -37,6 +37,7 @@ const thTH = {
     helpDocs: 'ขอความช่วยเหลือ',
     featureRequest: 'ขอฟีเจอร์ใหม่',
     starOnGitHub: 'ให้ดาวบน GitHub',
+    joinDiscord: 'เข้าร่วม Discord',
     create: 'สร้าง',
     edit: 'แก้ไข',
     delete: 'ลบ',