feat: calculation rules engine for decoupled cost attribution and chargeability

Introduces an admin-configurable rules engine that determines per-day cost
attribution (CHARGE/ZERO/REDUCE) and chargeability reporting (COUNT/SKIP)
for absence types (sick, vacation, public holiday). Includes shared types,
Zod schemas, Prisma model, rule matching with specificity scoring, default
rules, calculator integration, CRUD API router, seed data, chargeability
report integration, and admin UI.

283/283 engine tests, 209/209 API tests, 0 TS errors.

Co-Authored-By: claude-flow <ruv@ruv.net>

packages/db/prisma/schema.prisma

@@ -135,6 +135,24 @@ enum DispoImportSourceKind {
   ROSTER
 }
 
+enum AbsenceTrigger {
+  SICK
+  VACATION
+  PUBLIC_HOLIDAY
+  CUSTOM
+}
+
+enum CostEffect {
+  CHARGE
+  ZERO
+  REDUCE
+}
+
+enum ChargeabilityEffect {
+  COUNT
+  SKIP
+}
+
 enum DispoStagedRecordType {
   RESOURCE
   CLIENT
@@ -805,6 +823,7 @@ model Project {
   demandRequirements DemandRequirement[]
   assignments     Assignment[]
   estimates       Estimate[]
+  calculationRules CalculationRule[]
 
   createdAt       DateTime       @default(now())
   updatedAt       DateTime       @updatedAt
@@ -1315,6 +1334,37 @@ model SystemSettings {
   @@map("system_settings")
 }
 
+// ─── Calculation Rules ────────────────────────────────────────────────────────
+
+model CalculationRule {
+  id                    String               @id @default(cuid())
+  name                  String
+  description           String?
+
+  // ── Matching ──
+  triggerType           AbsenceTrigger
+  projectId             String?
+  orderType             OrderType?
+
+  // ── Effects ──
+  costEffect            CostEffect
+  costReductionPercent  Int?                 // only for REDUCE (0-100)
+  chargeabilityEffect   ChargeabilityEffect
+
+  // ── Ordering ──
+  priority              Int                  @default(0)
+  isActive              Boolean              @default(true)
+
+  project               Project?             @relation(fields: [projectId], references: [id])
+
+  createdAt             DateTime             @default(now())
+  updatedAt             DateTime             @updatedAt
+
+  @@index([triggerType, isActive])
+  @@index([projectId])
+  @@map("calculation_rules")
+}
+
 // ─── Audit Log ────────────────────────────────────────────────────────────────
 
 model AuditLog {

packages/db/src/seed.ts

@@ -293,6 +293,7 @@ async function main() {
   await prisma.resourceRole.deleteMany({});
   await prisma.vacation.deleteMany({});
   await prisma.vacationEntitlement.deleteMany({});
+  await prisma.calculationRule.deleteMany({});
   await prisma.project.deleteMany({});
   await prisma.resource.deleteMany({});
   await prisma.role.deleteMany({});
@@ -1215,6 +1216,40 @@ async function main() {
   }
   console.warn(`Vacations: ${vacationCount} created`);
 
+  // ── Calculation Rules (default set) ──────────────────────────────────────────
+  await prisma.calculationRule.createMany({
+    data: [
+      {
+        name: "Urlaub — Person chargeable, Projekt nicht belastet",
+        description: "Vacation days count toward chargeability but are not charged to the project.",
+        triggerType: "VACATION",
+        costEffect: "ZERO",
+        chargeabilityEffect: "COUNT",
+        priority: 0,
+        isActive: true,
+      },
+      {
+        name: "Krankheit — Person chargeable, Projekt nicht belastet",
+        description: "Sick days count toward chargeability but are not charged to the project.",
+        triggerType: "SICK",
+        costEffect: "ZERO",
+        chargeabilityEffect: "COUNT",
+        priority: 0,
+        isActive: true,
+      },
+      {
+        name: "Feiertag — kein Effekt",
+        description: "Public holidays are neither chargeable nor charged to projects.",
+        triggerType: "PUBLIC_HOLIDAY",
+        costEffect: "ZERO",
+        chargeabilityEffect: "SKIP",
+        priority: 0,
+        isActive: true,
+      },
+    ],
+  });
+  console.warn("Calculation rules: 3 default rules created");
+
   console.warn("Seed complete!");
 }