feat(build): add level-based parallel builds with --parallel and configurable concurrency

readme.hints.md

@@ -96,6 +96,18 @@ ts/
 - `@push.rocks/smartcli`: CLI framework
 - `@push.rocks/projectinfo`: Project metadata
 
+## Parallel Builds
+
+`--parallel` flag enables level-based parallel Docker builds:
+
+```bash
+tsdocker build --parallel           # parallel, default concurrency (4)
+tsdocker build --parallel=8         # parallel, concurrency 8
+tsdocker build --parallel --cached  # works with both modes
+```
+
+Implementation: `Dockerfile.computeLevels()` groups topologically sorted Dockerfiles into dependency levels. `Dockerfile.runWithConcurrency()` provides a worker-pool pattern for bounded concurrency. Both are public static methods on the `Dockerfile` class. The parallel logic exists in both `Dockerfile.buildDockerfiles()` (standard mode) and `TsDockerManager.build()` (cached mode).
+
 ## Build Status
 
 - Build: ✅ Passes