Create a multi-instance version of CrocoDash

## Use CrocoDash to Create a Multi-Instance (Ensemble) Run of Regional MOM6

**Summary:**
Ensemble data assimilation (DA) relies on running multiple model simulations (ensemble members) to estimate forecast uncertainty and improve analysis accuracy.
**CrocoDash** is an interactive tool for configuring, launching, and visualizing regional ocean model cases.

This project extends the existing [CrocoGallery notebook example](https://crocodile-cesm.github.io/CrocoGallery/notebooks/use_cases/three_boundary_from_t232.html), which currently demonstrates how to create a low-resolution MOM6 regional case for DA tool development. The goal is to enhance this workflow to support **multi-instance (ensemble) MOM6 runs** — where each instance represents a distinct ensemble member initialized with slightly different initial or boundary conditions.

A low-resolution configuration is ideal for early DA development because it reduces file sizes and run times, which allows developers to iterate over develop-run-develop cycle. Adding multi-instance capability will make this setup suitable for prototyping and testing ensemble DA workflows.

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### Motivation
Setting up an ensemble of regional MOM6 instances is essential for ensemble-based DA methods, including those used with DART or similar frameworks.
Currently, the CrocoDash workflow is limited to single-instance MOM6 configurations. Expanding it to support multi-instance cases will enable researchers to:
- Rapidly test ensemble data assimilation concepts using realistic MOM6 configurations.
- Reduce barriers to entry for regional DA experimentation.

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### Goals
- [ ] Extend the “Make a low-res domain for DA dev work!” notebook to support multi-instance MOM6 runs.
- [ ] Add CrocoDash UI options or configuration steps for setting `NINST_OCN` (number of instances).
- [ ] Run and verify multi-instance MOM6 simulations on a small (e.g., 3–5 member) ensemble.

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### Approach
- Use **CrocoDash** to configure MOM6 cases, modifying the generated `case` setup to include `NINST_OCN > 1`.
- Implement ensemble-aware file handling:
- Generate unique input directories and namelists for each instance.
- Link or copy common forcing and boundary files as needed.
- Integrate with CESM’s CIME layer (if applicable) to correctly handle `inst_suffixes` and per-member restarts.
- Use a small, low-resolution domain from the existing example to minimize cost.
- Test and validate by launching a short ensemble run (e.g., a few time steps) and verifying output structure and reproducibility.

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### Skills Needed or To be Gained in this Project
- Familiarity with **CrocoDash** and **CrocoGallery** workflows.
- Understanding of **CESM / MOM6 / CIME** configuration and build systems.
- Experience with **Python**, **Jupyter notebooks**, and **shell scripting**.
- (Optional) Background in **data assimilation** and **ensemble modeling** concepts.
- Basic **HPC job control** and file management skills.

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### Possible Challenges
- Managing directory structure and file linking for multiple instances.
- Limited documentation for regional multi-instance MOM6 runs within CESM frameworks.
- Boundary conditions for ensemble members
- Ensemble of atmospheric forcing vs single atmosphere forcing the ensemble of ocean models.

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### References
- [CrocoGallery: Low-Resolution MOM6 Setup Example](https://crocodile-cesm.github.io/CrocoGallery/notebooks/use_cases/three_boundary_from_t232.html)
- [CrocoDash Documentation](https://crocodile-cesm.github.io/CrocoDash)
- [MOM6 Documentation](https://mom6.readthedocs.io/en/latest/)
- [DART (Data Assimilation Research Testbed)](https://dart.ucar.edu/)
- CESM / CIME multi-instance configuration documentation