Add label metadata to example parameters for each fix category

[anth-volk]

Summary

This PR adds label metadata to example parameters across four categories that were identified as lacking proper labels. These fixes establish patterns for future work to ensure all parameters have human-readable labels.

Motivation: API v2 alpha aims to ensure all parameters have defined labels to improve trust for front-end users. Without proper labels, users see cryptic paths instead of meaningful descriptions.

Changes

Category	File	Fix
Breakdown without parent label	gov/states/wi/tax/income/deductions/standard/max.yaml	Added label
Bracket scale without label	gov/irs/credits/education/american_opportunity_credit/amount.yaml	Added label
Pseudo-breakdown	gov/irs/income/amt/exemption/amount.yaml	Added breakdown + label
Breakdown with range()	gov/irs/deductions/itemized/salt_and_real_estate/state_sales_tax_table/tax.yaml	Added breakdown_labels

Documentation

For detailed explanations of each category, before/after examples, and next steps, please see:
docs/PARAMETER_LABEL_METADATA_IMPROVEMENTS.md

Notes

• The breakdown_labels field is a new metadata field that requires a corresponding update to policyengine.py to be fully functional
• This PR fixes one example of each category; remaining parameters can be addressed in follow-up PRs

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.74%. Comparing base (fc2b613) to head (21b668b).
⚠️ Report is 42 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##              main    #7105       +/-   ##
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- Coverage   100.00%   75.74%   -24.26%     
============================================
  Files           10     3649     +3639     
  Lines          144    52526    +52382     
  Branches         0      263      +263     
============================================
+ Hits           144    39785    +39641     
- Misses           0    12718    +12718     
- Partials         0       23       +23     

Flag	Coverage Δ
unittests	75.74% <ø> (-24.26%)	⬇️

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