fix(ci): add .clusterfuzzlite/Dockerfile symlink -> Containerfile

The google/clusterfuzzlite build_fuzzers action hardcodes the path
.clusterfuzzlite/Dockerfile (no filename input); the repo ships the
SPDX-headed .clusterfuzzlite/Containerfile, so 'PR (address)' failed:

  ERROR: failed to read dockerfile: open Dockerfile: no such file

Add a tracked symlink Dockerfile -> Containerfile so clusterfuzzlite
resolves while the canonical file keeps the house-style Containerfile
name (Podman-not-Docker estate rule). Zero blast radius — nothing
references .clusterfuzzlite/Containerfile by name. Not a required
check; correctness/hygiene only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.clusterfuzzlite/Dockerfile

@@ -0,0 +1 @@
+Containerfile