Fix "Gewasresten achterlaten" visibility and residue removal calculation

[SvenVw]

Background & Motivation

In issue FDM-210, the "Gewasresten achterlaten" (m_cropresidue) input was made conditionally visible based on b_lu_eom_residue === 0. This implementation is incorrect for two reasons:

1. Wrong visibility condition: The input should only be visible when b_lu_croprotation === 'cereal'. Whether the EOM residue value is zero does not correctly capture which crops can leave residues — the crop rotation category is the right signal.
2. Wrong hidden value: When the input is hidden (non-cereal crops), m_cropresidue is currently defaulted to false. It should be undefined instead. Setting it to false incorrectly implies "residues are removed", which causes the nitrogen balance to calculate residue removal for non-cereal crops where this concept does not apply.

Requirements

UI

• The "Gewasresten achterlaten" input must only be visible when b_lu_croprotation === 'cereal'.
• When the input is hidden (not a cereal crop), the value of m_cropresidue must be undefined — not false.

Balance Calculations

The semantic meaning of m_cropresidue:

• true — user explicitly chose to leave residues on the field
• false — user explicitly chose to remove residues from the field
• undefined — no choice recorded (non-cereal crop); standard practice applies = residues are left on the field
• Organic matter supply by residues: supply must be calculated when m_cropresidue !== false (i.e., for both true and undefined).
• Nitrogen removal by residues: removal must only be calculated when m_cropresidue === false. For true or undefined, removal must be zero.

Affected Files

fdm-app

1. fdm-app/app/components/blocks/cultivation/card-details.tsx
   • Change the invisible class condition from !cultivation.b_lu_eom_residue → cultivation.b_lu_croprotation !== 'cereal'
   • Change the defaultValues / reset for m_cropresidue:
     • Before: !!cultivation.b_lu_eom_residue && (cultivation.m_cropresidue ?? false)
     • After: cultivation.b_lu_croprotation === 'cereal' ? (cultivation.m_cropresidue ?? undefined) : undefined
2. fdm-app/app/components/blocks/rotation/columns.tsx
   • Change the cell render condition for the m_cropresidue column:
     • Before: (props.row.original.b_lu_eom_residue ?? 0) !== 0
     • After: props.row.original.b_lu_croprotation === 'cereal'

fdm-calculator (verify, no change expected)

3. fdm-calculator/src/balance/nitrogen/removal/residue.ts
   • Already correctly handled. The guard if (cultivation.m_cropresidue !== false) returns zero for both true and undefined. No functional change needed, but add a test case that explicitly covers m_cropresidue === undefined resulting in zero removal.
4. fdm-calculator/src/balance/organic-matter/supply/residues.ts
   • Bug: Line 39 uses cult.m_cropresidue as a truthy check, so undefined currently yields zero EOM supply — this is wrong. Standard practice when m_cropresidue is undefined is that residues are left on the field, so supply should be calculated.
   • Change the condition:
     • Before: cultivationDetail?.b_lu_eom_residue != null && cult.m_cropresidue
     • After: cultivationDetail?.b_lu_eom_residue != null && cult.m_cropresidue !== false
   • Add a test case that verifies m_cropresidue === undefined results in the same EOM supply as m_cropresidue === true.

Acceptance Criteria

• The "Gewasresten achterlaten" checkbox is only shown for crops where b_lu_croprotation === 'cereal', both in the Cultivation Details card and in the Rotation Table.
• For non-cereal crops, m_cropresidue is stored/submitted as undefined (not false).
• The organic matter supply from residues is calculated when m_cropresidue !== false (covers both true and undefined).
• The nitrogen removal calculation returns 0 for cultivations where m_cropresidue is undefined or true.
• A test case exists in residue.test.ts that explicitly verifies m_cropresidue === undefined results in zero removal.
• Existing tests continue to pass.

Technical Notes

• b_lu_croprotation is a database enum defined in fdm-core/src/db/schema.ts with values: other, clover, nature, potato, grass, rapeseed, starch, maize, cereal, sugarbeet, alfalfa, catchcrop.
• Both CropRow and FieldRow in columns.tsx already carry b_lu_croprotation: string, so no data-fetching changes are needed.
• The Cultivation type in fdm-core/src/cultivation.types.d.ts already exposes b_lu_croprotation.