- deploy_cloudrun.py: FastAPI server adapted from deploy_modal.py for
  Cloud Run with L4 GPU. Same API contract, in-memory job tracking,
  GCS model download on startup, ensemble preset support.
- Dockerfile.cloudrun: CUDA 12.6 runtime, Python 3.11, FFmpeg, audio-separator[gpu]
- api_client.py: Add `preset` parameter to separate_audio() and
  separate_audio_and_wait() for ensemble preset-based separation
- deploy-to-cloudrun.yml: CI workflow to build and push to Artifact Registry

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Dockerfile: Download ensemble preset models (instrumental_clean +
  karaoke) during build. Eliminates cold-start model download.
- Remove google-cloud-storage dependency (no GCS model download needed)
- CI workflow: Switch to us-east4 (L4 GPU quota approved there)
- Reduce startup probe period (models pre-loaded, startup is fast)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Use COPY heredoc + separate RUN instead of inline python -c
which Docker can't parse with internal quotes/newlines.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Use Python 3.12 from deadsnakes PPA (onnxruntime-gpu needs >= 3.11)
- Use apt ffmpeg instead of downloading static build
- Add cloudbuild.yaml for building with baked models on GCP
  (E2_HIGHCPU_32 machine has enough RAM for model loading)
- Update GHA workflow to use Cloud Build instead of local Docker

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Cloud Build's Docker doesn't support BuildKit heredocs (COPY <<).
Use a separate script file instead.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Adds -p/--preset as a mutually exclusive option alongside -m/--model
and --models. Passes preset parameter through to API client.

Usage: audio-separator-remote separate song.mp3 -p instrumental_clean

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

When chaining separations (Stage 1 output → Stage 2 input), the input
filename contains stem markers like _(Vocals)_ that confuse the
Separator's stem grouping regex, causing it to only output 1 stem
instead of 2. Strip these markers before processing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>