feat: notifications in the app and, optionally, by e-mail

Derived from events and kept per person: whoever a ticket is assigned to,
whoever reports or works on it when it moves, fails QA or gets a comment,
and whoever joins a project. Never about what you did yourself, once per
event. They arrive live through a subscription to a bell in the header,
and are copied by e-mail to whoever turns it on when SMTP_URL is set.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/shared/ui/src/lib/icons.ts

@@ -17,6 +17,7 @@ import { MatIconRegistry } from '@angular/material/icon';
 export const APP_ICONS: Record<string, string> = {
   'arrow-forward':
     '<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round"><path d="M4 12h15M13 6l6 6-6 6"/></svg>',
+  bell: '<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round"><path d="M6 16V11a6 6 0 0 1 12 0v5l1.5 2h-15L6 16ZM10 20.5a2 2 0 0 0 4 0"/></svg>',
   briefcase:
     '<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round"><rect x="3" y="7" width="18" height="13" rx="2"/><path d="M9 7V5a2 2 0 0 1 2-2h2a2 2 0 0 1 2 2v2M3 12h18"/></svg>',
   buildings: