feat: Ein-/Auswinterung und Winterverluste je Volk

- WinterCheck per colony, winter and season (autumn/spring), every field
  editable; loss causes limited to the COLOSS monitoring categories.
- Summary per winter and apiary: loss rate lost/wintered, marked
  provisional while colonies are not yet checked in spring - an unchecked
  colony never counts as survived.
- A loss marks the colony deceased only on explicit request, in the same
  transaction and audited.
- Permissions winter-checks:read/create/update granted by migration to
  beekeeper and staff roles; winter checks included in backups.
- Page "Überwinterung": next action first, one button per row until the
  colony is wintered, German number format.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Backend/prisma/schema.prisma

@@ -93,6 +93,7 @@ model User {
   inspections           Inspection[]
   varroaMeasurements    VarroaMeasurement[]
   swarmControlChecks    SwarmControlCheck[]
+  winterChecks          WinterCheck[]
   treatments            Treatment[]
   feedings              Feeding[]
   harvests              Harvest[]
@@ -270,6 +271,7 @@ model Colony {
   inspections        Inspection[]
   varroaMeasurements VarroaMeasurement[]
   swarmControlChecks SwarmControlCheck[]
+  winterChecks       WinterCheck[]
   treatments         Treatment[]
   feedings           Feeding[]
   harvests           HarvestColony[]
@@ -595,6 +597,54 @@ model SwarmControlCheck {
   @@index([colonyId, date])
 }
 
+// ---------------------------------------------------------------------------
+// Ein- und Auswinterung, Winterverluste
+// ---------------------------------------------------------------------------
+
+enum WinterCheckSeason {
+  AUTUMN // Einwinterung
+  SPRING // Auswinterung
+}
+
+enum WinterOutcome {
+  SURVIVED
+  WEAK
+  LOST
+}
+
+// Verlustkategorien des COLOSS-Monitorings: totes/leeres Volk, unloesbares
+// Koeniginnenproblem, Naturereignis. Bewusst keine Diagnose (Varroa, Virus
+// ...): die gehoert, wenn ueberhaupt bekannt, in die Notiz.
+enum ColonyLossCause {
+  DEAD_OR_EMPTY
+  QUEEN_PROBLEM
+  NATURAL_DISASTER
+}
+
+// Eine Einwinterung und eine Auswinterung je Volk und Winter. winterYear ist
+// das Jahr, in dem der Winter beginnt (Winter 2026/27 = 2026).
+model WinterCheck {
+  id            String            @id @default(cuid())
+  colonyId      String
+  colony        Colony            @relation(fields: [colonyId], references: [id])
+  userId        String
+  user          User              @relation(fields: [userId], references: [id])
+  winterYear    Int
+  season        WinterCheckSeason
+  date          DateTime
+  occupiedSeams Int?
+  feedStockKg   Float?
+  queenPresent  Boolean?
+  outcome       WinterOutcome?
+  lossCause     ColonyLossCause?
+  notes         String?
+  createdAt     DateTime          @default(now())
+  updatedAt     DateTime          @updatedAt
+
+  @@unique([colonyId, winterYear, season])
+  @@index([winterYear])
+}
+
 // ---------------------------------------------------------------------------
 // Behandlung / Tierarzneimittel (Abschnitt 4.11)
 // ---------------------------------------------------------------------------