Mounted apps/ into ghost-dev container for pnpm 11 (#28210)

refs #28197, #28205. 

This fixes the `ghost-dev` compose for pnpm 11.

The dev Dockerfile (`docker/ghost-dev/Dockerfile`) only stages
`ghost/{core,i18n,parse-email-address}` `package.json`s at build time.
Compose then mounts `./ghost` into the container at runtime, which
exposes `ghost/admin`'s `workspace:*` deps (e.g.
`@tryghost/admin-x-framework` → lives in `apps/admin-x-framework/`).
pnpm 10 was lenient about the missing workspace packages; pnpm 11
strict-validates the workspace graph and `pnpm dev` fails instead of
being tolerated.