feat(units): add Unit-of-measure nomenclator (per-tenant, 3 langs)

- Migration: create `units` table + nullable unit_id FK on
  parts / wo_parts / purchase_items / labor_parts. Seeds ~11 standard
  units (buc/set/l/ml/kg/g/m/cm/m²/oră/pack) for every existing
  tenant and backfills unit_id by matching the legacy string `unit`
  column. Keeps `unit` string as fallback so old code paths keep
  rendering.
- Unit model: label(locale), forSelect(locale), labelFor(id, code)
  helpers. All 4 owner models get unitModel() relation + unitLabel()
  accessor.
- UnitResource under Depozit group with Filament UI: code, sort,
  is_active + separate name_ro/name_ru/name_en fields.
- Filament forms/tables updated: Part / PurchaseItem / LaborPart /
  WorkOrderPart now use Select('unit_id')->options(Unit::forSelect())
  for input and TextColumn->getStateUsing(unitLabel()) for display.
  Selecting a part auto-fills unit_id when the source has one.
- +10 translations for the new resource + defaults; nav.label
  'Unități de măsură' added to all 3 lang files.

All 306 tests pass.

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

app/Filament/Tenant/Resources/PartResource.php

@@ -93,7 +93,7 @@ class PartResource extends Resource
                 ->columns(4)
                 ->schema([
                     Forms\Components\TextInput::make('qty')->label(__('Cantitate'))->numeric()->default(0)->required(),
-                    Forms\Components\TextInput::make('unit')->label(__('UM'))->default('buc')->maxLength(16),
+                    Forms\Components\Select::make('unit_id')->label(__('UM'))->options(\App\Models\Tenant\Unit::forSelect())->searchable()->default(fn () => \App\Models\Tenant\Unit::where('code','buc')->value('id')),
                     Forms\Components\TextInput::make('min_qty')->label(__('Minim'))->numeric()->default(0),
                     Forms\Components\Toggle::make('is_active')->label(__('Activ'))->default(true),
                     Forms\Components\Toggle::make('is_published')
@@ -159,7 +159,7 @@ class PartResource extends Resource
                     ->alignRight()
                     ->color(fn ($state) => (float) $state > 0 ? 'info' : null)
                     ->toggleable(),
-                Tables\Columns\TextColumn::make('unit')->label(__('UM')),
+                Tables\Columns\TextColumn::make('unit_id')->label(__('UM'))->getStateUsing(fn ($record) => $record->unitLabel()),
                 Tables\Columns\TextColumn::make('location')->label(__('Loc.'))->placeholder('—'),
                 Tables\Columns\TextColumn::make('sell_price')->label(__('Preț vz.'))->money('MDL')->alignRight(),
                 Tables\Columns\IconColumn::make('is_published')->label(__('Magazin'))->boolean()->toggleable(),