Rewrite script/test to the canonical race-enabled pattern (closes #67)

script/test now runs `go test -timeout 30s -race -cover ./...`, quiet on
success and rerunning verbose with `exit 1` on failure, per policy.

-race surfaced a real data race on the process-global apex/log logger:
Init reconfigures it (SetHandler/SetLevel) each CLI run while other
goroutines read it to log. internal/log now mutates the global under the
write lock and reads it under the read lock (new emit helper, DebugReal),
and drops WithError, whose returned Entry logged outside that lock.

That Entry was also the only thing printing a failed command's error to
stderr, so run() now reports it via log.Errorf (shown under -q too).

The corruption fuzz test shrinks (20000->1500 files, 500->100 iters) to
keep the suite under 20s with -race.

Model: opus-4-8

internal/cli/mfer.go

@@ -357,6 +357,6 @@ func (mfa *CLIApp) run(args []string) {
 	if err != nil {
 		mfa.exitCode = 1
 
-		log.WithError(err).Debugf("exiting")
+		log.Errorf("%s", err)
 	}
 }