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 on failure. -race exposed a data race on the process-global apex/log logger: Init reconfigured it on every CLI run while other goroutines logged through it. internal/log now mutates the global under the write lock and reads it under the read lock; WithError is dropped because its Entry logged outside that lock, and run() reports a failed command's error via log.Errorf instead (still shown under -q). The corruption fuzz test is scaled to 1500 files / 100 iterations to fit the budget under -race; it pins the same claims at reduced breadth. Independent review ran the Docker lint gate uncached.

Model: opus-4-8 (implementation, review)
model: claude-fable-5

script/test

@@ -17,7 +17,12 @@ ensure_pb() {
 main() {
     cd "$ROOT"
     ensure_pb
-    go test -v --timeout 10s ./...
+    go test -timeout 30s -race -cover ./... ||
+        {
+            echo "--- Rerunning with -v for details ---"
+            go test -timeout 30s -race -v ./...
+            exit 1
+        }
 }
 
 main "$@"