All templates fail to build: unpinned devcontainers/base:ubuntu rolled to 26.04, breaking docker-in-docker

[pofallon]

All four templates fail to build. The docker-in-docker feature aborts during install:

(!) The 'moby' option is not supported on ubuntu 'resolute' because 'moby-cli' and related
    system packages are not available in that distribution.
(!) To continue, either set the feature option '"moby": false' or use a different base image.
ERROR: process "/bin/sh -c ... ./install.sh" did not complete successfully: exit code: 1

Cause

Every template pins the base image to the floating :ubuntu tag:

• src/full-stack/.devcontainer/devcontainer.json:3
• src/node-agentic/.devcontainer/devcontainer.json:3
• src/python-agentic/.devcontainer/devcontainer.json:3
• src/rust-agentic/.devcontainer/devcontainer.json:3

That tag has rolled forward to Ubuntu "resolute" (26.04). Canonical does not publish moby-cli or the related Moby packages for that release, and ghcr.io/devcontainers/features/docker-in-docker:2 defaults to moby: true — so it refuses to install. All four templates include docker-in-docker, so all four are affected. Nothing in the templates changed; the tag moved underneath them.

Suggested fix

Pin to the current LTS:

- "image": "mcr.microsoft.com/devcontainers/base:ubuntu",
+ "image": "mcr.microsoft.com/devcontainers/base:ubuntu-24.04",

Setting "moby": false also unblocks the build, but it swaps Moby for upstream Docker CE and leaves the templates on a pre-release distro where the other features are free to break on the next tag move. Pinning addresses the cause and makes builds reproducible; 26.04 can then be a deliberate bump once moby packages land.

Verified locally in a downstream project derived from python-agentic — pinning to ubuntu-24.04 builds clean through all features.