#2784 Docs: remove stale Docker Execution Driver section from the extension model reference

Problem

content/manual/reference/extensions/model.md (lines 457-460) still has a section about the removed Docker execution driver:

### Docker Execution Driver

The Docker execution driver uses `--allow-all`. `Deno.open()` on device nodes
works when using Docker placement.

swamp no longer has execution drivers. Remote execution replaced them (swamp-club#535), and extension drivers were removed from the CLI in swamp PR #2333 (swamp-club#1924). There is no raw or docker driver, no --driver flag, no driver: or driverConfig: fields, and no --allow-all execution mode. See design/enablers/remote-execution.md in the swamp repo, "No execution drivers" (around line 405).

Isolation now comes from how a worker is deployed: a containerized worker is selected for a step with labels. A worker runs the method in-process in its own swamp process, which is the same compiled binary. So the "Device Node Limitation" section above still applies on workers, and the claim that Deno.open() on device nodes works in a container is not supported by the current design.

Suggested fix

1. Delete the ### Docker Execution Driver section.
2. Optionally add one sentence to "Device Node Limitation" or "Subprocess Workaround": for a step that needs a host device, run it on a worker deployed on that host (or in a container with the device mounted), select it with labels, and use the Deno.Command subprocess workaround there. Link content/manual/reference/remote-execution/workflow-placement.md and content/manual/how-to/worker-fleets/docker.md, after checking that those pages describe label-based placement.
3. Grep content/manual for driver, driverConfig, driversDir, extensions/drivers and "execution driver". This section was the only stale hit when checked. The data.latest("driver", ...) example in reference/workflows.md:1038 is just a model named driver and should stay.

Related

swamp-club#2748 cleans up the same stale driver references in the swamp repo (bundled skill, README, help text). This is the manual-side companion.