M1.4.3 Add simple snow albedo parameterization

Summary

Implement a simple snow albedo representation suitable for coupling snow to the existing energy-balance model.

Purpose

Represent the high reflectivity of snow and, if desired and feasible, its decline with aging between snowfall events.

Tasks

• Implement either fixed snow albedo for v1, or simple fresh-snow to aged-snow decay
• Define whether new snowfall resets snow albedo fully or partially.
• Document the selected scheme.

Acceptance criteria

• Fresh snowfall increases snow albedo if a prognostic scheme is used.
• Snow albedo decays toward an aged-snow value if aging is used.
• Snow albedo stays within prescribed bounds.
• The chosen scheme is documented and wired into effective surface albedo calculations.

Suggested tests

• Fixed-albedo mode.
• Aging without snowfall.
• Albedo refresh after snowfall.

Locate the existing energy-balance model and effective surface albedo calculations first; the issue does not name specific files or entry points. Choose and document either fixed snow albedo or an aging scheme, wire it into effective albedo, and add tests covering the selected mode, bounds, aging, and snowfall refresh behavior.