Caddyfile: point the shared family login at dankuser too

The other vhosts (gitea, grafana, search, ...) now use username 'dankuser'
with CADDY_BASICAUTH_HASH, which is set to the same hash as the homepage
(dankpassword.123). So the whole protected surface logs in as
dankuser / dankpassword.123; the operator /admin/ page still uses frank.
Updated the two tests that asserted the old 'dank' username.

tests/caddyfile.bats

@@ -72,7 +72,7 @@ CADDYFILE="$REPO_ROOT/dankclaw/Caddyfile"
         echo "Caddyfile: bcrypt prefix before REPLACE_WITH_HASH (double-prefix regression)"
         return 1
     fi
-    grep -qE 'dank REPLACE_WITH_HASH' "$CADDYFILE"
+    grep -qE 'dankuser REPLACE_WITH_HASH' "$CADDYFILE"
 }
 
 @test "compose no longer defines the quadlet-replaced services" {