fix: mapping field import behavior

[mjnagel]

Description

This PR adjusts the behavior around mapping/justifications on imports:

1. Adjusts column order to match the control view (mappings after custom)
2. Changes behavior so that mapping is an extra place to place a field, rather than moving it there. This allows for keeping the original field on a different tab, while also using it to auto-populate mapping justifications.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (security config, docs update, etc)

Checklist before merging

• Test, docs, adr added or updated as needed
• Contributor Guide Steps followed

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.11%. Comparing base (22171ed) to head (b2a053c).

Files with missing lines	Patch %	Lines
cli/server/spreadsheetRoutes.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #164      +/-   ##
==========================================
+ Coverage   58.98%   59.11%   +0.12%     
==========================================
  Files          20       20              
  Lines        3672     3664       -8     
  Branches      451      451              
==========================================
  Hits         2166     2166              
+ Misses       1504     1496       -8     
  Partials        2        2              

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[github-actions]

🎉 This PR is included in version 0.3.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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