Update broadband simulation to use BA18 + CB14 model from site amplification package

[lispandfound]

As described, but I took the opportunity to further refactor bb-sim:

1. bb-sim is now dask powered, so requires less memory on clusters by making use of chunking.
2. bb-sim now handles mismatched sample rates between low frequency and high frequency via signal resampling.
3. bb-sim now embeds the vs30 and all the site amplification parameters used into the output.

[gemini-code-assist]

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[Copilot]

Pull request overview

Updates the broadband simulation pipeline to use the BA2018 + CB2014 site amplification models from the site-calculation package, while refactoring bb-sim to operate lazily with dask/xarray for lower memory usage and adding metadata to outputs.

Changes:

• Refactors broadband merging to dask/xarray, including station-chunked processing and per-chunk site amplification + filtering.
• Adds signal resampling to handle LF/HF mismatched sample rates and embeds Vs30 + site amp parameters in output metadata.
• Introduces SiteAmpModel enum and extends broadband parameter schemas/defaults to support BA2018/CB2014 selection.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
workflow/scripts/bb_sim.py	Reworks broadband merge to dask/xarray, adds resampling/alignment, and applies BA2018/CB2014 amplification from site-calculation.
workflow/schemas.py	Adds SiteAmpModel and tightens broadband parameter validation (including new taper params).
workflow/realisations.py	Updates BroadbandParameters dataclass to include fhightop, fmax, and typed site_amp_version.
workflow/default_parameters/v24_2_2_4/defaults.yaml	Removes per-version bb defaults (now inherited from root).
workflow/default_parameters/v24_2_2_2/defaults.yaml	Removes per-version bb defaults (now inherited from root).
workflow/default_parameters/v24_2_2_1/defaults.yaml	Removes per-version bb defaults (now inherited from root).
workflow/default_parameters/root/defaults.yaml	Adds/updates broadband defaults including BA2018 model selection and taper frequencies.
uv.lock	Adds site-calculation and updates lock entries accordingly.
pyproject.toml	Declares dependency on site-calculation>=2026.7.1.
tests/test_realisation.py	Updates broadband parameter serialization test for new fields and enum.

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