Diagnostic cloud-scatterplots-cli-ta expects mip=realm for OBS

## Describe the bug

I get the following error message (below) when trying to run the `cloud-scatterplots-cli-ta` diagnostic with a CMIP7 model, where the relevant error message (one of several) is:
```
2026-07-03 22:57:48,876 UTC [3019873] ERROR No files were found for Dataset:
{'dataset': 'ISCCP-FH',
'project': 'OBS',
'mip': 'atmos',
'short_name': 'rsutcs',
'alias': 'OBS_ISCCP-FH',
'derive': True,
'frequency': '',
'long_name': 'TOA Outgoing Clear-Sky Shortwave Radiation',
'modeling_realm': ['atmos'],
'original_short_name': 'rsutcs',
'preprocessor': 'zonal_mean',
'recipe_dataset_index': 3,
'standard_name': 'toa_outgoing_shortwave_flux_assuming_clear_sky',
'tier': 2,
'timerange': '1996/2016',
'type': 'sat',
'units': 'W m-2',
'version': 'v0'}
session: 'recipe_20260703_225747',
using data sources:
- data source: LocalDataSource(name='local', project='OBS', priority=1, rootpath=PosixPath('/fs/site7/eccc/crd/cccma/users/scrd115/REF_v4/climate-ref/.ref/cache/esmvaltool/datasets/ESMValTool/OBS'), dirname_template='Tier{tier}/{dataset}', filename_template='{project}_{dataset}_{type}_{version}_{mip}_{short_name}[_.]*nc', ignore_warnings=[])
message: No files found matching glob pattern /fs/site7/eccc/crd/cccma/users/scrd115/REF_v4/climate-ref/.ref/cache/esmvaltool/datasets/ESMValTool/OBS/Tier2/ISCCP-FH/OBS_ISCCP-FH_sat_v0_atmos_rsutcs[_.]*nc
```

My interpretation of the filename, having `_atmos_` (instead of `_Amon_` where the diagnostic is run for a CMIP6 model), is that this diagnostic expects a different `mip` facet value when comparing to CMIP7? this is a problem, as the data provided (via the fetch function) has the filename structure where `mip=`

**out.log** contents attached

## System

- OS: Linux
- Python version: 3.11.9

[out.log](https://github.com/user-attachments/files/29650772/out.log)

Start with the cloud-scatterplots-cli-ta diagnostic and the attached out.log, then trace how its OBS dataset metadata sets the mip facet. Compare the requested atmos path with the fetch function's CMOR6 table_id filename structure; done means the diagnostic locates the provided OBS files for CMIP7 without breaking the CMIP6 case.

Written by the indexing model from the issue text.