Release v0.4.0

This cuts v0.4.0 from main at 19dad8df. The release adds the monorepo workspace (one clone, a worktree per MR, a reap), the GPU lane through up --accelerator, --control-replicas for a compact OpenShift cluster, and the single scan gate with skillspector v2.11.1. It moves gitlab-dev-stack to 1.8.1 and ends with Changelog entries for every change since 0.3.0. The knob rename is breaking: the old names are no longer read, and the entry says to rename them before you upgrade.

Before this MR: the case 17 fidelity repeat on merged main ended KEEP, and the cap sentence now sits under the worktree-add command because the repeat missed it. A live just lab validate passed on the caproni base at main and again with dev-stack 1.8.1, and drift-check read 155/155. just ci is green. The tag follows the merge and is annotated, with the 0.4.0 section as its body.

• Put the worktree cap where a one-MR reader sees it
• Record the monorepo fidelity repeat
• Fill the changelog for every change since 0.3.0
• Release 0.4.0