refactor: rename Fabled Assistant to Fabled Scribe

Updates user-visible branding across frontend (PWA manifest, page title,
Settings, push fallback), backend (email templates and subjects, LLM
system prompt, CalDAV displayname, SMTP from-name default), README,
quickstart compose, and MCP server description.

Also updates the CI image path and quickstart image reference to
git.fabledsword.com/bvandeusen/fabledscribe in preparation for the
Forgejo repo rename. Internal Python package, env vars, and database
schema unchanged.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/public/sw.js

@@ -12,7 +12,7 @@ self.addEventListener('push', event => {
           return;
         }
       }
-      return self.registration.showNotification(data.title || 'Fabled Assistant', {
+      return self.registration.showNotification(data.title || 'Scribe', {
         body: data.body || '',
         icon: '/favicon.ico',
         badge: '/favicon.ico',