feat(driver): CloudDriver forwards X-Owner-Id (DRO-1682)

[lutz-grex]

Summary

• CloudDriver.__init__ gains an optional owner_id: str | None = None parameter.
• When user_id is set and owner_id is provided, X-Owner-Id is added to default_headers alongside the existing X-User-ID header. When owner_id is None, behavior is unchanged (header omitted).
• This lets the cloud device driver forward the tenancy header that devices-api now requires (devices-api #503, merged/live on dev), fixing dev device-driving 400s for the tasks-api agent.

Release / rollout note (action required by a human)

• This PR alone does not fix the live dev incident. A new mobilerun release (e.g. 0.6.0rc6) must be cut from this change, and tasks-api's pyproject.toml pin (mobilerun[langfuse]==0.6.0rc5) must be bumped to that release, before owner_id can actually be passed through and take effect.
• Until that release + pin bump happens, the corresponding tasks-api change is being tracked as a comment/placeholder in PR Automation #224 (lucius/dro-1682-tasks-owner-threading) — it is NOT wired up yet because the currently-pinned 0.6.0rc5 has no owner_id param and would TypeError if called with one.
• Do not merge or release this yet — prepared as part of the dev-incident fix, still needs review/coordination with the release + pin-bump step.

Test plan

• Added two unit tests to tests/test_cloud_driver_sdk.py:
  • test_owner_id_forwarded_as_x_owner_id_header — constructs CloudDriver(device_id="d", user_id="u", owner_id="o") and asserts the client's default_headers contains X-Owner-Id: o (no network call, mocked AsyncMobilerun).
  • test_owner_id_omitted_when_not_provided — asserts X-Owner-Id is absent when owner_id is not passed.
• uv run pytest — full suite green (220 passed).

Part of DRO-1682