test(e2e): make Docker runtime available to Symphony workers

[moncher-dev]

Problem

The Docker E2E runner cannot start in the current Symphony worker environment because Docker Compose is installed but the Docker daemon at unix:///var/run/docker.sock is unreachable.

Evidence

While validating #879 on 2026-09-05, pnpm e2e:claude was run twice in isolation. Both attempts exited with the runner's prerequisite status 69:

[e2e] Docker runtime unavailable: Docker Compose is installed, but the Docker daemon is not reachable.
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

The full unit-test, lint, typecheck, and build suite passes. This follow-up tracks the shared-host Docker availability issue rather than the code under #879.

Expected

Workers assigned integration-boundary changes can execute repository Docker E2E runners, or receive a documented environment capability signal before attempting them.

[moncher-dev]

Added to the board in Backlog for triage visibility, not as work to pick up.

Docker on this host is a settled operator decision: it is not installed, deliberately. The exit 69 prerequisite status you hit is the runner's preflight working as designed, not a defect — and specifically not a defect in the PR that was under review when it surfaced. CI's container-smoke job is the authoritative container check for this repository, and it passed on #885's head.

Leaving this open for @hojinzs to close or re-scope. Workers should not act on it: parking it in Backlog means the agent ignores it, and no future review should treat a local exit 69 at preflight as a blocker.