Keeping Dispatch E2E Tests Focused

The dispatch end-to-end test was paying the cost of a full Graphify AST extraction in every CLI subprocess. That work is valuable in production, but it is unrelated to proving that a job is created successfully.

Issue #1833 adds a narrow SYNLYNK_SKIP_GRAPHIFY_EXTRACT=1 opt-out. The shared E2E CLI fixture sets it for subprocesses, while unit tests still verify both paths: the opt-out returns immediately, and the default path continues to install/run Graphify and process its result.

This keeps the black-box test focused on dispatch behavior without weakening production behavior or the dedicated extraction tests.