Concrete Log subclass for the engine debug log. Captures time, level,
and subsystem prefix per entry; stack-trace continuation lines attach
to the triggering ERROR entry via PatternParser's append-on-no-match
behaviour. Detectors: filename match on DebugLog-server.txt plus two
content signatures (the version=X.Y.Z+hash banner and the level/
subsystem/f/t/st header shape). Pattern constants live in
src/Pattern/ProjectZomboid/DebugServerPattern.php with named groups
ready for analyser use in phase B. Synthetic fixture under
test/src/Games/ProjectZomboid/fixtures/ uses zeroed identifiers and
placeholder paths.
