feat: per-row and global discount with margin validation

Parts (wo_parts) already had discount_pct; now also added to wo_works.
Labor catalog gets a cost_price field as the hard minimum sell floor.

- WorkOrderWork: discount_pct + cost_price fields; total calculation
  now includes discount: hours × price_per_hour × (1 − disc/100)
- Labor model: cost_price field (used to pre-fill work rows and validate)
- WorksRelationManager: discount_pct field with live helper text showing
  effective price + margin %; validation blocks save if below buy cost
  or below company min_discount_margin_pct; "Reducere globală" header
  action applies % to all work rows (skips rows that would breach limits)
- PartsRelationManager: same validation on existing discount_pct field;
  helper text (🟢/🟠/🔴) shows effective price + margin in real time;
  "Reducere globală" header action for all parts
- Settings page: new "Reduceri & limite preț" section with
  min_discount_margin_pct — 0 = no limit, >0 = hard block below that %
- LaborResource form: cost_price field

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

app/Filament/Tenant/Resources/LaborResource.php

@@ -71,6 +71,8 @@ class LaborResource extends Resource
                     Forms\Components\TextInput::make('fixed_price')->label(__('Preț fix (MDL)'))->numeric()->default(0)
                         ->visible(fn (Schemas\Components\Utilities\Get $get) => $get('pricing_mode') === 'fixed'),
                     Forms\Components\TextInput::make('price')->label(__('Preț orientativ (MDL)'))->numeric()->default(0),
+                    Forms\Components\TextInput::make('cost_price')->label(__('Preț cost (MDL)'))->numeric()->default(0)
+                        ->helperText(__('Costul intern — limita minimă sub care nu se poate vinde cu reducere.')),
                     Forms\Components\Toggle::make('is_active')->label(__('Activă'))->default(true),
                 ]),
             Forms\Components\Textarea::make('notes')->label(__('Observații'))->columnSpanFull()->rows(2),