fix: implement table:"-" field exclusion

[masonkatz]

Summary

• omit fields tagged with table:"-" from text tables
• preserve correct spacing when a skipped or empty column is last
• document and test that JSON and YAML retain original struct fields

Fixes #3

Validation

• make test
• make lint (currently reports five pre-existing goconst findings on origin/main)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.60%. Comparing base (ab3a1e6) to head (625b66f).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #7      +/-   ##
==========================================
+ Coverage   80.76%   81.60%   +0.83%     
==========================================
  Files           8        8              
  Lines         286      299      +13     
==========================================
+ Hits          231      244      +13     
  Misses         51       51              
  Partials        4        4              

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[masonkatz]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved the merge conflict in text.go — the annotationsFor function from main was merged alongside the lastVisibleColumn/visible additions from this branch. All tests pass (commit 625b66f).