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>

src/fabledassistant/services/calendar_sync.py

@@ -66,7 +66,7 @@ async def setup_user_calendar(user_id: int) -> bool:
   <set>
     <prop>
       <resourcetype><collection/><C:calendar/></resourcetype>
-      <displayname>Fabled Assistant</displayname>
+      <displayname>Fabled Scribe</displayname>
     </prop>
   </set>
 </mkcol>""",