chore: remove the linked desktop drivers from core #5391

Part of #5200.

User Story

As an OpenShell Maintainer I want the desktop drivers to exist in their own repository so that their ownership and maintenance can be considered separately to core OpenShell. Core must build without them.

Problem Statement

After Docker and Podman launch as external drivers, core still contains the linked-factory features and two reverse dependencies: openshell-supervisor-network depends on openshell-driver-vm for an allocation-tracking test helper, and openshell-driver-vm depends on openshell-driver-podman for socket detection.

Impact / Why This Matters

Core cannot build or test without the desktop driver crates until these ties are cut. This is what makes the later repository move a directory move.

Proposed Design

Remove the linked-factory features. Move the allocation-tracking helper out of openshell-driver-vm and socket detection out of openshell-driver-podman. Core's own tests that construct real desktop drivers use lightweight in-test doubles.

Acceptance Criteria

• Core's gateway and tests no longer depend on the desktop driver crates.
• Core's e2e runs on Kubernetes, with the desktop drivers exercised as external targets.

Alternatives Considered

• Keep the linked features behind a flag. Leaves core compiled against the drivers, which is what feat: move the desktop compute drivers to the ai-openshell/desktop repository #5200 is meant to end.