Add --access-log <path> (env ZDDC_ACCESS_LOG). When set, every access-
log record is written as a JSON line to the configured file in
addition to the existing slog.Default() stderr output. Empty (default)
keeps the prior behavior — stderr only.
Rotation via gopkg.in/natefinch/lumberjack.v2:
100 MB per file, 10 backups, 90-day max age, gzip rotated files.
Operator usage (e.g. behind a Caddy/quadlet stack):
zddc-server --access-log /srv/.zddc.d/logs/access.log ...
Architecture:
AccessLogMiddleware now takes an optional *slog.Logger. main.go wires
it via setupAccessAuditLog() which builds a slog.JSONHandler over a
lumberjack rotator. Stderr emission stays via slog.Default(); the
audit logger gets the same fields in line-delimited JSON, the format
every standard log shipper (Vector, Loki, fluentbit, journalbeat)
parses natively.
Tests cover the audit logger receiving the same email/path/status
fields as the stderr stream.