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/en-US.ts

@@ -37,6 +37,7 @@ const enUS = {
     helpDocs: 'Get Help',
     featureRequest: 'Feature Request',
     starOnGitHub: 'Star on GitHub',
+    joinDiscord: 'Join our Discord',
     create: 'Create',
     edit: 'Edit',
     delete: 'Delete',