fix(docker): package selected external plugins in source-built images (#103629)

* build(docker): package selected external plugins

* test(docker): auto-clean plugin fixture

* fix(docker): preserve selected image provenance

* fix(docker): accept manifest-only plugin selections

* fix(docker): resolve selected plugin manifest ids

* fix(docker): isolate resolved plugin selection

docs/docs_map.md

@@ -4216,6 +4216,7 @@ Do not edit it by hand; run `pnpm docs:map:gen`.
   - H3: Manual flow
   - H3: Upgrading container images
   - H3: Environment variables
+  - H3: Source-built images with selected plugins
   - H3: Observability
   - H3: Health checks
   - H3: LAN vs loopback