Faza 3.3: Depozit — Furnizori + Catalog piese + Achiziții

Schema:
- suppliers: name, contact, phone/email/website, pay_terms, delivery_days,
  rating (1-5), discount_pct, categories (JSON), is_active, notes
- parts: name, article (UNIQUE per tenant), brand, category, qty/unit/min_qty,
  buy_price/sell_price, location (rack/bin), barcode, preferred_supplier_id,
  is_active. Index pe (company_id, category) și (company_id, is_active).
- purchases: număr unique per tenant + an, supplier_id, status workflow
  (draft/ordered/received/cancelled), order/expected/received/paid_at, total
- purchase_items: name, article, qty, unit, buy_price, total auto, received bool;
  link opțional la part_id
- wo_parts + part_id: linkare opțională la catalog (alter migration)

Modele cu logică:
- Part::adjustStock($delta) — modifică qty cu validare ≥ 0
- Part::isLow() / isOut() helpers
- Purchase::markReceived() — atomic: marchează items ca received + creste qty
  pe pieces din catalog (DB::transaction)
- WorkOrderPart::updating event — la trecerea status='installed' decrementează
  stoc auto. La revenire (ex: storno) incrementează la loc.
- PurchaseItem::saving — total = qty * buy_price; recalc parent total

Filament resources (group Depozit):
- SupplierResource: form 3 secțiuni, rating ★★★★★, TagsInput pentru categorii
- PartResource: form 4 secțiuni, badge nav cu nr. piese sub stoc minim,
  filtre low_stock + out_of_stock, coloană qty colorată după stoc
- PurchaseResource: form antet + RelationManager Items.
  Action 'Recepționează' care apelează markReceived() — un click = stoc actualizat

WorkOrder PartsRelationManager updated:
- Selector din catalog (Part::active) cu stoc afișat
- Auto-fill name/article/brand/unit/buy_price/sell_price din piesa selectată
- Helper text: la status='installed' se scade din stoc

Widget low-stock:
- TableWidget pe dashboard tenant, listează piesele cu qty <= min_qty
- Span full, sortat după qty (cele mai critice sus)

Seed:
- 2 furnizori (AutoParts Moldova SRL ★5, Inter Cars Moldova ★4)
- 5 piese demo: Ulei Shell, Filtru Mann, Plăcuțe Brembo, Antigel (qty=0!), Bujii NGK
- 1 achiziție recepționată (P-26-0001) cu 2 articole linked la catalog

Total Filament tenant routes: 63 (de la 31).

app/Models/Tenant/WorkOrderPart.php

@@ -20,7 +20,7 @@ class WorkOrderPart extends Model
     ];
 
     protected $fillable = [
-        'company_id', 'work_order_id',
+        'company_id', 'work_order_id', 'part_id',
         'name', 'article', 'brand',
         'qty', 'unit', 'buy_price', 'sell_price',
         'discount_pct', 'total', 'status', 'notes',
@@ -39,6 +39,11 @@ class WorkOrderPart extends Model
         return $this->belongsTo(WorkOrder::class);
     }
 
+    public function part(): BelongsTo
+    {
+        return $this->belongsTo(Part::class);
+    }
+
     protected static function booted(): void
     {
         static::saving(function (self $row) {
@@ -46,6 +51,22 @@ class WorkOrderPart extends Model
             $disc = (float) $row->discount_pct;
             $row->total = round($sub * (1 - $disc / 100), 2);
         });
+
+        // When a part is marked installed, decrement catalog stock once.
+        static::updating(function (self $row) {
+            $wasInstalled = $row->getOriginal('status') === 'installed';
+            $isInstalled = $row->status === 'installed';
+            if (! $wasInstalled && $isInstalled && $row->part_id) {
+                $part = Part::find($row->part_id);
+                $part?->adjustStock(-(float) $row->qty);
+            }
+            // If reverting from installed → restore stock
+            if ($wasInstalled && ! $isInstalled && $row->part_id) {
+                $part = Part::find($row->part_id);
+                $part?->adjustStock((float) $row->qty);
+            }
+        });
+
         static::saved(fn (self $row) => $row->workOrder?->recalcTotal());
         static::deleted(fn (self $row) => $row->workOrder?->recalcTotal());
     }