Fix three AMT function bugs against 2025 Form 6251

[martinholmer]

Bug Fixes

• (a) Remove stale medical add-back from itemizer AMTI build. TCJA/OBBBA
  harmonized the AMT and regular Schedule A medical floors at 7.5% of
  AGI, so the 2025 Form 6251 Part I has no medical add-back line. The
  stale 2.5% add-back encoded the pre-TCJA 10%-vs-7.5% floor
  differential. Drop c17000 from the AMT signature.

• (b) Correct Part III "skip 20%-bracket / reform-4th-bracket" test from
  line17 == line32 to line22 == line32. The form's gate compares the
  cap-gains-eligible portion (line 22) to the sum of 0%+15% amounts
  (line 32), not the ordinary-income portion (line 17). Under current
  law (AMT_CG_brk3 = 9e+99) the prior test set line33 = 0 when it
  should have computed line22 - line32 > 0.

• (c) Subtract standard deduction in non-itemizer AMTI. Form 6251 line 1
  equals Form 1040 line 15 = AGI - (STD or itemized) - QBID. The
  prior code encoded the pre-TCJA "AMT disallows STD" rule, which
  overstated AMTI for high-income non-itemizers near the exemption
  phaseout (TCJA permitted STD for AMT).

Changes in Expected Test Results

• Refresh cpscsv_agg_expect.csv, reforms_expect.csv, test_reforms_cps
  expected diffs, and test_utils.test_create_tables expected values.

• Regenerate CPS+TMD .tables baselines for 2025-2035 (.params.*
  baselines unchanged because no policy parameters changed).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (eb10fa4) to head (2ba5fc9).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #3049   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           13        13           
  Lines         2721      2721           
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  Hits          2721      2721           

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

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