Stage 5.1 — Warehouse ERP: batches + FIFO + reservations + multi-warehouse

Schema:
- warehouses (multi-warehouse, code unique per company, is_default)
- part_batches (lot per receipt, qty_in/qty_remaining, buy_price, FIFO-indexed)
- warehouse_events (immutable ledger: opening/receipt/issue/transfer/adjustment/write_off)
- part_reservations (per-WO allocations from specific batches, active/consumed/released)
- companies.default_warehouse_id + parts.qty_reserved

Backfill: 1 default warehouse + 1 opening batch per existing part per company.

WarehouseService:
- receive / issue (FIFO) / reserve / release / consume / transfer / adjust
- DB::transaction + lockForUpdate on batch rows
- InsufficientStockException with requested + available context
- Auto-syncs parts.qty as aggregate cache (source of truth = sum(qty_remaining))

WO integration:
- WorkOrderPart created/updated → reserve from FIFO batches
- WorkOrderPart deleted → release
- WorkOrder status=done → consume reservations into issue events
- WorkOrder status=cancelled → release reservations

Filament:
- WarehouseResource (CRUD)
- BatchesRelationManager on PartResource (FIFO list with qty_remaining + cost)
- "Recepție" action on parts list → calls WarehouseService::receive
- qty_reserved column added on parts list

Tests (8 new, all pass):
- receipt creates batch + event
- FIFO order verified across 3 batches with different received_at
- InsufficientStockException on over-issue
- Reservations block other reservations but don't deplete on-hand
- WO done consumes; WO cancelled releases
- Batches tenant-isolated
- Transfer between warehouses with weighted-avg cost

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/Models/Tenant/Part.php

@@ -5,6 +5,7 @@ namespace App\Models\Tenant;
 use App\Models\Concerns\BelongsToTenant;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\HasMany;
 use Illuminate\Database\Eloquent\SoftDeletes;
 
 class Part extends Model
@@ -18,7 +19,7 @@ class Part extends Model
 
     protected $fillable = [
         'company_id', 'name', 'article', 'brand', 'category',
-        'qty', 'unit', 'min_qty',
+        'qty', 'qty_reserved', 'unit', 'min_qty',
         'buy_price', 'sell_price',
         'location', 'barcode', 'preferred_supplier_id',
         'is_active', 'notes',
@@ -26,6 +27,7 @@ class Part extends Model
 
     protected $casts = [
         'qty' => 'decimal:2',
+        'qty_reserved' => 'decimal:3',
         'min_qty' => 'decimal:2',
         'buy_price' => 'decimal:2',
         'sell_price' => 'decimal:2',
@@ -37,6 +39,35 @@ class Part extends Model
         return $this->belongsTo(Supplier::class, 'preferred_supplier_id');
     }
 
+    public function batches(): HasMany
+    {
+        return $this->hasMany(PartBatch::class);
+    }
+
+    public function reservations(): HasMany
+    {
+        return $this->hasMany(PartReservation::class);
+    }
+
+    public function events(): HasMany
+    {
+        return $this->hasMany(WarehouseEvent::class);
+    }
+
+    /** Live total across all batches of all warehouses (source of truth). */
+    public function qtyOnHand(?int $warehouseId = null): float
+    {
+        $q = $this->batches()->newQuery()->where('part_id', $this->id);
+        if ($warehouseId) $q->where('warehouse_id', $warehouseId);
+        return (float) $q->sum('qty_remaining');
+    }
+
+    /** Available for new reservations = on hand − already reserved. */
+    public function qtyAvailable(?int $warehouseId = null): float
+    {
+        return max(0.0, $this->qtyOnHand($warehouseId) - (float) $this->qty_reserved);
+    }
+
     public function isLow(): bool
     {
         return (float) $this->qty <= (float) $this->min_qty;
@@ -47,6 +78,11 @@ class Part extends Model
         return (float) $this->qty <= 0;
     }
 
+    /**
+     * Legacy direct-stock adjustment.
+     * NOTE: this only moves the cached `qty` column. Real stock changes
+     * should go through WarehouseService so batches + events stay in sync.
+     */
     public function adjustStock(float $delta, ?string $reason = null): void
     {
         $this->qty = max(0, (float) $this->qty + $delta);