feat(04-01): InventoryItem and StockMovement schema with enums

- Add ItemTrackingType (SERIALIZED/BATCH), ItemCondition, MovementType, LocationType enums
- Add InventoryItem model with dual tracking (serialized by serial number, batch by quantity)
- Add StockMovement model as immutable movement ledger (no updatedAt)
- Add recordedMovements relation on User model
- Indexes on tenantId, itemType, trackingType, inventoryItemId, movementType

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

prisma/schema.prisma

@@ -142,6 +142,32 @@ enum CompensationModel {
   HYBRID
 }
 
+enum ItemTrackingType {
+  SERIALIZED
+  BATCH
+}
+
+enum ItemCondition {
+  NEW
+  REFURBISHED
+  USED
+  DAMAGED
+}
+
+enum MovementType {
+  RECEIVED
+  ISSUED
+  RETURNED
+  DISPOSED
+  TRANSFERRED
+}
+
+enum LocationType {
+  WAREHOUSE
+  TECHNICIAN
+  SUBSCRIBER
+}
+
 // =============================================================================
 // MODELS
 // =============================================================================
@@ -401,6 +427,8 @@ model User {
   createdJobOrders  JobOrder[]     @relation("JobOrderCreatedBy")
   /// Technician profiles for this user (one per tenant, enforced by @@unique([tenantId, userId]))
   technicianProfiles TechnicianProfile[]
+  /// Stock movements performed/recorded by this user
+  recordedMovements StockMovement[] @relation("MovementPerformedBy")
 
   createdAt DateTime @default(now())
   updatedAt DateTime @updatedAt
@@ -855,3 +883,73 @@ model JobTypeRate {
   /// RLS-ready index — always present on tenant-scoped models
   @@index([tenantId])
 }
+
+/// An InventoryItem represents a piece of ISP equipment (router, ONU, cable, etc.).
+/// Serialized items have unique serial numbers and are tracked individually.
+/// Batch items (consumables like cables, connectors) are tracked by type+quantity.
+/// Stock levels are NEVER stored — always derived from movement history.
+model InventoryItem {
+  id            String           @id @default(uuid())
+  tenantId      String
+  /// Human-readable name (e.g., "Huawei HG8145V5 ONU")
+  name          String
+  /// Category type (e.g., "Router", "ONU", "Cable", "Connector")
+  itemType      String
+  /// Brand/model identifier for serialized items (optional for batch)
+  model         String?
+  /// Unique serial number — required for SERIALIZED, null for BATCH
+  serialNumber  String?
+  trackingType  ItemTrackingType
+  /// Purchase cost per unit (2 decimal places)
+  purchaseCost  Decimal?         @db.Decimal(10, 2)
+  purchaseDate  DateTime?
+  warrantyExpiry DateTime?
+  /// Soft-delete: inactive items are not shown in active lists
+  isActive      Boolean          @default(true)
+  createdAt     DateTime         @default(now())
+  updatedAt     DateTime         @updatedAt
+
+  movements     StockMovement[]
+
+  /// Serial numbers must be unique within a tenant (only enforced for non-null values)
+  @@unique([tenantId, serialNumber])
+  /// RLS-ready index — always present on tenant-scoped models
+  @@index([tenantId])
+  @@index([tenantId, itemType])
+  @@index([tenantId, trackingType])
+}
+
+/// A StockMovement is an immutable record of inventory movement.
+/// Stock levels are derived by aggregating movements — no mutable quantity columns.
+/// RECEIVED movements auto-post journal entries (DR 1200 Equipment Inventory, CR 2010 AP).
+model StockMovement {
+  id               String         @id @default(uuid())
+  tenantId         String
+  /// The inventory item this movement affects
+  inventoryItemId  String
+  inventoryItem    InventoryItem  @relation(fields: [inventoryItemId], references: [id])
+  movementType     MovementType
+  /// Quantity moved — always 1 for SERIALIZED items, variable for BATCH
+  quantity         Int            @default(1)
+  /// Condition of the item at time of movement
+  condition        ItemCondition?
+  /// Source location (null for RECEIVED — items come from external supplier)
+  fromLocationType LocationType?
+  fromLocationId   String?
+  /// Destination location (null for DISPOSED — items leave the system)
+  toLocationType   LocationType?
+  toLocationId     String?
+  notes            String?
+  /// Journal entry created for RECEIVED movements (DR 1200, CR 2010)
+  journalEntryId   String?
+  /// The user who recorded this movement
+  performedById    String
+  performedBy      User           @relation("MovementPerformedBy", fields: [performedById], references: [id])
+  /// Immutable — no updatedAt. Movements cannot be modified, only new movements added.
+  createdAt        DateTime       @default(now())
+
+  /// RLS-ready index — always present on tenant-scoped models
+  @@index([tenantId])
+  @@index([inventoryItemId])
+  @@index([tenantId, movementType])
+}