refactor(moss_tts_nano): migrate to Pipeline + Deploy schema

Follow-up to #2958. MOSS-TTS-Nano was authored before the schema refactor
and still shipped as a legacy stage_configs yaml; this aligns it with the
same layout the 5 migrated TTS models now use.

- vllm_omni/model_executor/models/moss_tts_nano/pipeline.py declares
  MOSS_TTS_NANO_PIPELINE (single LLM_AR stage, owns_tokenizer, audio
  output, stop_token_ids=[2] as a hard EOS backstop).
- vllm_omni/deploy/moss_tts_nano.yaml holds runtime knobs (max_num_seqs,
  gpu_memory_utilization, enforce_eager, default_sampling_params,
  skip_mm_profiling); trust_remote_code stays at deploy top-level.
- vllm_omni/config/pipeline_registry.py registers the entry so the lazy
  registry can resolve it.
- moss_tts_nano/__init__.py exports MossTTSNanoForGeneration (VoxCPM2 pattern).
- Removed vllm_omni/model_executor/stage_configs/moss_tts_nano.yaml.

Examples, shell scripts, READMEs, and buildkite-invoked tests are
updated to use `vllm serve <model> --omni` / `--deploy-config`
(auto-load kicks in; no --stage-configs-path or --trust-remote-code).

Signed-off-by: Yueqian Lin <linyueqian@outlook.com>

examples/online_serving/moss_tts_nano/README.md

@@ -29,14 +29,13 @@ Features:
 ## Launch the Server
 
 ```bash
-vllm-omni serve OpenMOSS-Team/MOSS-TTS-Nano \
-    --stage-configs-path vllm_omni/model_executor/stage_configs/moss_tts_nano.yaml \
-    --omni \
-    --port 8091 \
-    --trust-remote-code \
-    --enforce-eager
+vllm serve OpenMOSS-Team/MOSS-TTS-Nano --omni --port 8091
 ```
 
+The deploy config at `vllm_omni/deploy/moss_tts_nano.yaml` auto-loads; no
+`--stage-configs-path`, `--trust-remote-code`, or `--enforce-eager` flags
+are needed.
+
 Or use the convenience script:
 
 ```bash

examples/online_serving/moss_tts_nano/run_gradio_demo.sh

@@ -11,16 +11,12 @@ MODEL="${MODEL:-OpenMOSS-Team/MOSS-TTS-Nano}"
 PORT="${PORT:-8091}"
 GRADIO_PORT="${GRADIO_PORT:-7860}"
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
-REPO_ROOT="$(cd "$SCRIPT_DIR/../../.." && pwd)"
 
 echo "Starting MOSS-TTS-Nano server (port $PORT)..."
 FLASHINFER_DISABLE_VERSION_CHECK=1 \
-vllm-omni serve "$MODEL" \
-    --stage-configs-path "$REPO_ROOT/vllm_omni/model_executor/stage_configs/moss_tts_nano.yaml" \
+vllm serve "$MODEL" \
     --host 0.0.0.0 \
     --port "$PORT" \
-    --trust-remote-code \
-    --enforce-eager \
     --omni &
 SERVER_PID=$!
 

examples/online_serving/moss_tts_nano/run_server.sh

@@ -9,16 +9,11 @@ set -e
 
 MODEL="${MODEL:-OpenMOSS-Team/MOSS-TTS-Nano}"
 PORT="${PORT:-8091}"
-SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
-REPO_ROOT="$(cd "$SCRIPT_DIR/../../.." && pwd)"
 
 echo "Starting MOSS-TTS-Nano server with model: $MODEL"
 
 FLASHINFER_DISABLE_VERSION_CHECK=1 \
-vllm-omni serve "$MODEL" \
-    --stage-configs-path "$REPO_ROOT/vllm_omni/model_executor/stage_configs/moss_tts_nano.yaml" \
+vllm serve "$MODEL" \
     --host 0.0.0.0 \
     --port "$PORT" \
-    --trust-remote-code \
-    --enforce-eager \
     --omni