#309 Clarify soil water fraction notation in documentation

[ayushman1210]

Summary

• What: Updated mathematical notation for "soil water fraction" across parameter documentation and model structure descriptions to clarify unclipped and clipped variants.
• Motivation: Addresses confusion regarding the overloaded term "soil water content fraction", distinguishing between the absolute soil water content ($W_{\text{soil}}$), the unbounded fraction ($f_{\text{WHC}}$), and the internally clipped fraction used for dependency functions ($f_{\text{WHC}^*}$).

How was this change tested?

This is a documentation-only change. No code, configuration files, or model logic was modified, so existing tests are unaffected.

Reproduction steps

N/A

Related issues

• Fixes Clarify soil water fraction notation in documentation #309

Checklist

• Related issues are listed above. PRs without an approved, related issue may not get reviewed.
• PR title has the issue number in it ("[#] <concise description of proposed change>")
• Tests added/updated for new features (if applicable)
• Documentation updated (if applicable)
• docs/CHANGELOG.md updated with noteworthy changes
• Code formatted with clang-format (run git clang-format if needed)

[Alomir]

I'm marking this as 'requested changes' pending @dlebauer's thoughts on proposed changes.

[dlebauer]

👍 I agree with the proposed changes.

[ayushman1210]

hey @Alomir @dlebauer please review this pr when you have some free time
thanks !!