style(ui): float auth/security cards to match mockup shadow language

Login/register, forgot-password, reset-password, verify-email, and the
2FA/sessions settings cards all used a bare MuiPaper (1px border, no
shadow) predating this session's theme foundation. MuiPaper itself
stays untouched (it's a lower-level primitive used too broadly across
the app -- menus, popovers -- to safely restyle globally), so these
specific card instances get the same explicit no-border/floating-shadow
treatment already applied screen-by-screen elsewhere this session.

Static shadow value again, not theme.vars.customShadows -- inline sx
callbacks execute against whatever theme is in context, and none of
this repo's tests wrap components in a ThemeProvider (see fc56f94).

job-tracker-ui/src/components/TwoFactorSettingsCard.tsx

@@ -184,7 +184,7 @@ export default function TwoFactorSettingsCard() {
   const isRecoveryStep = flow === "enable-recovery" || flow === "regenerate-recovery";
 
   return (
-    <Paper sx={{ mt: 2, p: 2 }}>
+    <Paper sx={{ mt: 2, p: 2.5, borderRadius: 4, border: "none", boxShadow: "0px 1px 2px 0px rgba(15,23,42,0.04), 0px 8px 24px -12px rgba(15,23,42,0.12)" }}>
       <Typography variant="h6" sx={{ mb: 1 }}>
         {t("twoFactorSectionTitle")}
       </Typography>