Remove CEF: the web content crate, ElyMark's page, their packaging, licences and tests (C14.5)

PRD and agents.md name the native route; ElyMail's body will not use
CEF or Electron. ElyMark's package carries the KaTeX fonts' OFL.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/scripts/linux-distros.sh

@@ -31,7 +31,7 @@ docker build -q -t ely-smoke-fedora - >/dev/null <<'EOF'
 FROM fedora:44@sha256:43b29f65a41eb9c35e1cd5323e3bdf3b655c2357a9f4f1ff2f9c2798e5045d80
 RUN dnf install -y -q xorg-x11-server-Xvfb mesa-vulkan-drivers xwd xwininfo && dnf clean all
 EOF
-# As the work dir's owner: Git and CEF refuse root.
+# As the work dir's owner: Git refuses others' repos.
 inside='set -euo pipefail
 slug=$1 work=$2 file=$3
 shift 3