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/PartBatch.php

@@ -0,0 +1,51 @@
+<?php
+
+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;
+
+class PartBatch extends Model
+{
+    use BelongsToTenant;
+
+    protected $fillable = [
+        'company_id', 'part_id', 'warehouse_id', 'supplier_id',
+        'batch_ref', 'qty_in', 'qty_remaining', 'buy_price',
+        'received_at', 'notes',
+    ];
+
+    protected $casts = [
+        'qty_in' => 'decimal:3',
+        'qty_remaining' => 'decimal:3',
+        'buy_price' => 'decimal:2',
+        'received_at' => 'datetime',
+    ];
+
+    public function part(): BelongsTo
+    {
+        return $this->belongsTo(Part::class);
+    }
+
+    public function warehouse(): BelongsTo
+    {
+        return $this->belongsTo(Warehouse::class);
+    }
+
+    public function supplier(): BelongsTo
+    {
+        return $this->belongsTo(Supplier::class);
+    }
+
+    public function reservations(): HasMany
+    {
+        return $this->hasMany(PartReservation::class, 'batch_id');
+    }
+
+    public function isDepleted(): bool
+    {
+        return (float) $this->qty_remaining <= 0;
+    }
+}