feat: add dev container for full-stack development (#861)

Layer the frontend toolchain on top of the existing release builder
image so a single container covers Go, C support-layer and web
development, with the builder image remaining the single source of
truth for the cross toolchain, Go and MaixCDK.

- Mount the workspace at /home/build/NanoKVM, where the Makefile and
  support/sg2002/build expect it, and resync MaixCDK components via
  update_lib on create so C builds never use stale sources
- Install Node from official dist tarballs (integrity-checked, pinned
  to the major used by CI), with NODE_DIST_MIRROR / NPM_REGISTRY /
  BASE_IMAGE build args for restrictive or mirrored corporate networks
- Export the MaixCDK virtualenv via remoteEnv so non-interactive
  processes (tasks, extensions, exec) get it too; make
  updateRemoteUserUID explicit since the published builder image bakes
  the CI runner's uid
- Run pnpm non-interactively during post-create (no TTY) and give the
  skeleton-less home a standard ~/.profile -> ~/.bashrc chain
- Make the web toolchain convention explicit via package.json engines
  (Node >= 22, pnpm >= 11, matching CI) and document it in web/README
- Document the dev container in the README, point server/README at the
  container flow that works on any host OS, and ignore .pnpm-store/

server/README.md

@@ -64,7 +64,7 @@ turn:
 
 ## Compile & Deploy
 
-Note: Use Linux operating system (x86-64) with Go 1.25 or newer. This build process is not compatible with ARM, Windows or macOS.
+Note: The manual steps below require a Linux x86-64 host with Go 1.25 or newer; they are not compatible with ARM, Windows or macOS. With Docker you can skip them entirely and use the containerized flow instead — the root [Makefile](../Makefile) (`make shell`) or the dev container (see "Development" in the root [README](../README.md)) — which works on any host OS; run `server/build.sh` inside the container for a release-equivalent build.
 
 1. Install the Toolchain
     1. Download the toolchain from the following link: [Download Link](https://sophon-file.sophon.cn/sophon-prod-s3/drive/23/03/07/16/host-tools.tar.gz).