feat: language switcher on portal + apply_margin re-added to Plată & total

Two fixes:

== 1. Language switcher (RO/RU/EN) in portal headers ==

New partial resources/views/partials/lang-switcher.blade.php with two
visual styles:
- style='chip' (default) — white-tinted glass for colored headers
  (shop nav bar, tracking page hero)
- style='light' — outlined buttons for pale backgrounds (invitation
  accept card)

Each button is a POST form to the existing /locale/{lang} route which:
- puts locale in session
- persists to user.locale if authenticated
- redirects back to the same page

Included in:
- resources/views/shop/layout.blade.php (right side of top nav,
  after login/register)
- resources/views/tracking/show.blade.php (top-right of hero header,
  absolutely positioned)
- resources/views/invitations/accept.blade.php (top-right of card,
  above welcome heading, light style)

Current locale button is highlighted (opaque white on colored bg /
blue on pale bg). Others are muted until hovered.

Two new translation keys:
- portal.common.language (RO: Limbă / RU: Язык)

== 2. apply_margin toggle back in "Plată & total" ==

Previous session's edit didn't persist to the file. Now confirmed in
place: WorkOrderResource form's "Plată & total" section shows a
"Aplică marjă internă" toggle between discount_pct and
override_margin_pct. Gated by FINANCE_VIEW_INTERNAL_MARGIN so only
owner / admin / manager / accountant see it. Default = true.

When toggled off on a Fișă, WorkOrderWork::saving hook writes
salary_base = total for every line on that WO (no reduction).
Backend logic already in place — this commit fixes the missing UI
control.

Suite: 303 passed (840 assertions). Unchanged — refactor + view only.

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

app/Filament/Tenant/Resources/WorkOrderResource.php

@@ -114,6 +114,11 @@ class WorkOrderResource extends Resource
                 ->schema([
                     Forms\Components\Select::make('pay_status')->options(WorkOrder::PAY_STATUSES)->default('unpaid')->required(),
                     Forms\Components\TextInput::make('discount_pct')->label('Discount %')->numeric()->default(0),
+                    Forms\Components\Toggle::make('apply_margin')
+                        ->label('Aplică marjă internă')
+                        ->default(true)
+                        ->helperText('On = din prețul manoperelor se scade marja pentru salariu. Off = manopere la cost (salariu pe Total integral).')
+                        ->visible(fn () => auth()->user()?->canDo(\App\Auth\Permissions::FINANCE_VIEW_INTERNAL_MARGIN) ?? false),
                     Forms\Components\TextInput::make('override_margin_pct')->label('Marjă internă (%) — override')
                         ->numeric()->step(0.01)->minValue(0)->maxValue(90)
                         ->placeholder('Ex: 25')