🐛 BUG: large context sent to docker, in containers-template

### Which template does this pertain to?

containers-template

### What versions are you using?

wrangler 4.61.0, Docker for mac 4.57.0

### What operating system and version are you using?

macOS 26

### Please provide a link to a minimal reproduction (optional)

_No response_

### Describe the Bug

`node_modules` contains workerd + vitest + esbuild + wrangler + etc, which quick amounts to 200MB.
When doing `npx wrangler deploy`, the directory is compressed (tar) and sent to the Docker engine.
This can be controlled with `.dockerignore`, or better yet by moving the Dockerfile to a subdirectory.

I think the Go server template would benefit from either:
- having `Dockerfile` in container_src
- adding `.node_modules` / `.git` to `.dockerignore`.

These only affect build speed (and so, deployments). Discoverability / explainability of what's running in Isolates vs Container may benefit/suffer from this.

In my small test env, cached builds take ~8s, drops down to ~1.6s with `node_modules/` in `.dockerignore`.

### Please provide any relevant error logs

_No response_