FEAT-5: Probeverpaarung entry point from animal detail (?parent=) + stored-vs-engine Farbschlag mismatch hint

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

gerbil-manager-web/src/pages/GenetikPage.tsx

@@ -1,6 +1,9 @@
 import { useMemo, useState } from 'react'
+import { useSearchParams } from 'react-router-dom'
 import { de } from '../strings/de'
 import { breed, fromDisplayString, type BreedingResult } from '../genetics'
+import { getGerbil } from '../api/gerbils'
+import { useApi } from '../hooks/useApi'
 import ParentSelector, { type ParentValue } from '../components/ParentSelector'
 import AnimalPicker from '../components/AnimalPicker'
 import { isValidGenotype } from '../format/genotypeText'
@@ -18,6 +21,22 @@ export default function GenetikPage() {
   const [mother, setMother] = useState<ParentValue>(EMPTY_PARENT)
   const [showGenotypes, setShowGenotypes] = useState(false)
 
+  // Pre-fill a parent when arriving from an animal's detail page (?parent=<id>).
+  // Gender decides the side: female -> Mutter, otherwise Vater.
+  const [searchParams] = useSearchParams()
+  const parentId = searchParams.get('parent')
+  const prefill = useApi(
+    () => (parentId ? getGerbil(parentId) : Promise.resolve(null)),
+    [parentId],
+  )
+  const [prefilledFor, setPrefilledFor] = useState<string | null>(null)
+  if (prefill.data && prefilledFor !== prefill.data.id) {
+    setPrefilledFor(prefill.data.id)
+    const value: ParentValue = { genotype: prefill.data.genotype ?? '', animalName: prefill.data.name }
+    if (prefill.data.gender === 'female') setMother(value)
+    else setFather(value)
+  }
+
   const bothValid = isValidGenotype(father.genotype) && isValidGenotype(mother.genotype)
 
   const result: BreedingResult | null = useMemo(() => {