Support regional retrievals and standard plots

[astrojaket]

What changed

• add one-region, diluted one-region, and two-region YAML retrieval models
• allow each region to select independent temperature-profile, chemistry, and cloud models
• resolve output, scratch, and cache paths relative to the configuration directory by default
• remove repetitive hardcoded run directories from shipped configurations
• add automatic spectral posterior plots with a 68% envelope, native-opacity-grid spectra, and binned-model squares
• add temperature-pressure profile and posterior corner plots
• retain and integrate the deferred optimal-estimation improvements already present in the worktree
• document the configuration and plotting behavior, including SSH-only GitHub operations

Why

Retrieval configurations should be portable between local machines and DiRAC, and two-profile retrievals need explicit per-region physics. Standard posterior diagnostics should also be produced automatically.

User impact

A retrieval can be launched with:

python run_retrieval.py --config configuration.yaml

Generated directories remain local to the configuration unless the top-level path settings explicitly override them.

Validation

• full suite before final documentation-only edit: 463 passed, 1 skipped
• directly affected suite after staging: 72 passed
• git diff --check: passed