fix(deploy): exclude macOS AppleDouble files from deploy archive

When tar runs on macOS it embeds ._* resource-fork sidecars next to each
file. These ended up under l4d2web/alembic/versions/ on the target and
alembic tried to import them as migration modules, failing with
"source code string cannot contain null bytes". Set COPYFILE_DISABLE=1
and add an --exclude '._*' so the archive is portable.

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

deploy/deploy-test-server.sh

@@ -21,13 +21,14 @@ cleanup() {
 }
 trap cleanup EXIT INT HUP TERM
 
-tar -czf "$archive" \
+COPYFILE_DISABLE=1 tar -czf "$archive" \
     --exclude .git \
     --exclude .venv \
     --exclude __pycache__ \
     --exclude .pytest_cache \
     --exclude '*.egg-info' \
     --exclude 'l4d2web.db*' \
+    --exclude '._*' \
     -C "$repo_root" .
 
 remote_tmp=$(ssh "$target" 'mktemp -d')