VS6: cursor-cloud behavioral e2e + docs

[Praneeth16]

Parent

omnigent-ai#1148

What to build

Per-harness behavioral e2e (SDK boundary mocked, no live cloud calls in CI) proving the streamed events + final PR-bearing response, plus the env-setup-gap error path. Document the new harness: GitHub + dashboard-onboarding prerequisite and the v1 scope boundary.

Acceptance criteria

• e2e: a turn streams assistant text and resolves with a PR link (mocked SDK)
• e2e: 'repo not set up' surfaces the onboarding-URL error
• docs describe GitHub/onboarding prerequisite + deferred scope

Blocked by

• VS1: cursor-cloud harness selectable end-to-end (tracer bullet) #1
• VS2: cursor-cloud repo/ref resolution (cwd remote + override) #2
• VS3: cursor-cloud model resolution + /model override #3
• VS4: cursor-cloud full stream mapping + env-setup-gap error #4
• VS5: cursor-cloud onboarding polish (readiness, install, CLI) #5