Add comprehensive comparison of intensity.py between current and tng_grism branches

[Copilot]

Compares kl_tools/intensity.py implementations across branches to document architectural evolution and guide branch selection.

Summary Document

Created INTENSITY_COMPARISON.md covering:

• Architectural patterns: Current branch uses ImagePars abstraction with dependency injection; tng_grism uses direct datacube coupling
• Class-level changes: All major classes (IntensityMap, InclinedExponential, BasisIntensityMap, IntensityMapFitter) differ significantly in constructor signatures and render methods
• New capabilities: Current adds CompositeIntensityMap for exp+basis models; tng_grism adds GMixModel stub
• Design focus: Current optimized for single-line analysis with cleaner abstractions; tng_grism designed for multi-line spectroscopy with per-line morphology

Key Distinctions

Current branch (~1,279 lines):

# Modern: parameterized, reusable
imap = InclinedExponential(flux=1e4, hlr=3.5)
image, continuum = imap.render(image_pars, theta_pars, pars, weights=weights, mask=mask)

tng_grism branch (~1,275 lines):

# Legacy: datacube-coupled, multi-line aware
imap = InclinedExponential(datacube, {'flux': 1e4, 'hlr': 3.5, 'em_PaA_hlr': 4.0})
images = imap.render(theta_pars, datacube, pars)  # Returns dict with per-line images

Document includes migration path, usage recommendations, and detailed change breakdown across ~750 modified lines.

Original prompt

On intensity.py, Summary the difference between this intensity.py file and the intensity.py file in the tng_grism branch

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