Resolves conflicts in:
- vllm_omni/diffusion/registry.py: keep both LancePipeline (HEAD)
and MingImagePipeline (main) entries.
- vllm_omni/diffusion/models/bagel/bagel_transformer.py: take main's
simpler cfg_batched payload; HEAD referenced undefined locals.
Also strips vllm_omni/deploy/lance.yaml -- Lance is single-stage
diffusion, so its engine knobs (pipeline=lance, enforce_eager,
trust_remote_code, max_num_seqs=1, ...) flow directly to Omni(...)
/ vllm-omni serve instead of through a deploy YAML.
create_default_diffusion builds the stage config from those kwargs.
Touched: examples/offline_inference/lance/{end2end,gradio_demo}.py,
tests/e2e/online_serving/test_lance.py, tests/helpers/stage_config.py.
Signed-off-by: lishunyang12 <lishunyang12@163.com>