Web: drop avatars, show navigation on shared project/report pages ...

- remove GnAvatar from the shell footer and the settings profile card
- AppShell falls back to a plain centered body when nobody is logged in, so
  ProjectPage and ReportPage can wrap it too: logged-in users get the nav
  shell on share-token pages, anonymous visitors keep the bare layout
- pages no longer carry their own max-width/padding (the shell body owns it)

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