Fix payment amount editable + discount live recalculation

- PaymentsRelationManager: remove broken default() closure on amount;
  use fillForm() on CreateAction instead (correct Filament API) so the
  modal pre-fills with remaining balance (total - paid) but field stays
  fully editable; add minValue/step for numeric UX
- WorkOrderResource: discount_pct is now live(onBlur) with afterStateUpdated
  that recomputes works+parts+subcontract minus discount and sets the
  total field immediately — no Save required to see the effect

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

app/Filament/Tenant/Resources/WorkOrderResource/RelationManagers/PaymentsRelationManager.php

@@ -28,11 +28,9 @@ class PaymentsRelationManager extends RelationManager
             Forms\Components\TextInput::make('amount')
                 ->label(__('Sumă'))
                 ->numeric()
-                ->required()
-                ->default(function (RelationManager $livewire): float {
-                    $wo = $livewire->getOwnerRecord();
-                    return max(0.0, (float) $wo->total - $wo->paidAmount());
-                }),
+                ->minValue(0.01)
+                ->step(0.01)
+                ->required(),
             Forms\Components\Select::make('method')
                 ->options(\App\Support\I18n::opts(Payment::METHODS))
                 ->default('cash')
@@ -59,6 +57,12 @@ class PaymentsRelationManager extends RelationManager
                 Actions\CreateAction::make()
                     ->label(__('Adaugă plată'))
                     ->modalHeading(__('Adaugă plată la fișă'))
+                    ->fillForm(function (RelationManager $livewire): array {
+                        $wo = $livewire->getOwnerRecord();
+                        return [
+                            'amount' => max(0.0, round((float) $wo->total - $wo->paidAmount(), 2)),
+                        ];
+                    })
                     ->mutateFormDataUsing(function (array $data, RelationManager $livewire): array {
                         $wo = $livewire->getOwnerRecord();
                         $data['client_id'] = $wo->client_id;