feat: marjă internă per mechanic — hidden margin on labor

Client sees only Total. Salary is calculated from salary_base = client_price
× (1 − margin/100). Margin never appears in customer-facing surfaces (PDF,
tracking JSON, portal).

Terminology: "marjă internă" — internal profit margin. NOT VAT/TVA. Never
called NDS/TVA anywhere in the code to avoid confusion with real Moldova
tax reporting (Doc 19/1C integration).

== Configuration ==

Fallback chain (in MarginResolver::resolve):
  1. WorkOrder.override_margin_pct — per-Fișă for special contracts/VIP
  2. User.internal_margin_pct — per-mechanic (main setting)
  3. Company.settings.default_internal_margin_pct — tenant default
  4. 0.0 — no margin

Example (mechanic Andrei with 20% margin):
  User enters price_per_hour = 250 for 1h diagnosis
  → total = 250 (what client sees, goes into PDF)
  → salary_base = 250 × 0.80 = 200 (what mechanic gets salaried on)
  → applied_margin_pct = 20 (frozen)

If admin later changes Andrei's margin to 40%, the row's salary_base does
NOT change — history is immutable. Only new rows use the new margin.
Solves the retroactive-recompute problem for closed payroll periods.

== salary_base freeze semantics ==

wo_works gains 2 columns:
  salary_base decimal(10,2) nullable
  applied_margin_pct decimal(5,2) nullable

Frozen at save time by WorkOrderWork::saving hook. Recomputes only if
total OR master_id changes (i.e., someone actively edits the price or
reassigns the mechanic — in those cases we WANT the salary_base to
follow). Legacy rows (before this feature) have null salary_base;
PayrollCalculator falls back to total for them.

== PayrollCalculator uses salary_base ==

Previously: sum(wo_works.total) × works_pct → gave the mechanic a cut
of the price INCLUDING margin.

Now: sum(salary_base ?? total) × works_pct → the cut is from the
labor rate excluding margin.

Impact: for a 250 lei diagnosis at 20% margin with 50% payroll cut, the
mechanic gets 200 × 50% = 100 lei (was 250 × 50% = 125 lei). The shop
keeps the 50 lei margin regardless of the payroll %.

== RBAC gate ==

New permission FINANCE_VIEW_INTERNAL_MARGIN. Assigned to owner + admin +
manager + accountant in seed matrix. Not granted to mechanic,
receptionist, or viewer — those roles never see the "Bază salariu"
disclosure line or the margin % fields.

== UI surfaces ==

UserResource — new "Salariu & marjă" section (visible only with
FINANCE_VIEW_INTERNAL_MARGIN):
  - Tarif orar (MDL)
  - Marjă internă (%) with helper text explaining the -X% semantics
  - Placeholder tells manager the exact formula

WorkOrderResource form — new override_margin_pct field in the "Plată &
total" section, gated by same permission. Helper text: "Doar pentru
cazuri speciale. Lasă gol pentru a folosi marja mecanicului."

WorksRelationManager (WO edit page) — Total column now shows a gray
subtitle line "Bază salariu: 200.00 MDL · marjă 20%" ONLY for users
with FINANCE_VIEW_INTERNAL_MARGIN. Everyone else sees just Total.

== Contract tests: NO leak ==

InternalMarginTest verifies with black-box grepping that:
- WorkOrderPdfService::generate output contains NONE of
  {salary_base, internal_margin, applied_margin_pct, marja intern,
  Bază salariu}
- /api/track/{token} JSON payload contains NONE of the same terms
- wo_parts table has no salary_base column (margin ONLY on labor)
- Changing mechanic.internal_margin_pct after work is saved does NOT
  rewrite the historical salary_base (frozen)
- WO override wins over mechanic margin (contract-priced clients)
- Fallback chain: WO → mechanic → company default → 0

== Suite ==
298 passed (828 assertions). Was 285. +13 InternalMarginTest.

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

app/Auth/Permissions.php

@@ -40,6 +40,7 @@ class Permissions
     // Finance
     public const FINANCE_VIEW_OVERVIEW = 'finance.view_overview';
     public const FINANCE_VIEW_PL = 'finance.view_pl';
+    public const FINANCE_VIEW_INTERNAL_MARGIN = 'finance.view_internal_margin';
     public const FINANCE_CREATE_PAYMENT = 'finance.create_payment';
     public const FINANCE_DELETE_PAYMENT = 'finance.delete_payment';
     public const FINANCE_CREATE_EXPENSE = 'finance.create_expense';
@@ -91,7 +92,7 @@ class Permissions
             self::WORK_ORDERS_EDIT, self::WORK_ORDERS_DELETE, self::WORK_ORDERS_CHANGE_STATUS,
             self::WORK_ORDERS_APPROVE_DISCOUNT_5, self::WORK_ORDERS_APPROVE_DISCOUNT_20,
             self::WORK_ORDERS_APPROVE_DISCOUNT_ANY, self::WORK_ORDERS_PRINT,
-            self::FINANCE_VIEW_OVERVIEW, self::FINANCE_VIEW_PL, self::FINANCE_CREATE_PAYMENT,
+            self::FINANCE_VIEW_OVERVIEW, self::FINANCE_VIEW_PL, self::FINANCE_VIEW_INTERNAL_MARGIN, self::FINANCE_CREATE_PAYMENT,
             self::FINANCE_DELETE_PAYMENT, self::FINANCE_CREATE_EXPENSE, self::FINANCE_EXPORT,
             self::SALARIES_VIEW_OWN, self::SALARIES_VIEW_ALL, self::SALARIES_CALCULATE, self::SALARIES_MARK_PAID,
             self::INVENTORY_VIEW, self::INVENTORY_CREATE_PART, self::INVENTORY_EDIT_PART, self::INVENTORY_DELETE_PART,
@@ -154,7 +155,7 @@ class Permissions
             self::WORK_ORDERS_EDIT, self::WORK_ORDERS_CHANGE_STATUS,
             self::WORK_ORDERS_APPROVE_DISCOUNT_5, self::WORK_ORDERS_APPROVE_DISCOUNT_20,
             self::WORK_ORDERS_PRINT,
-            self::FINANCE_VIEW_OVERVIEW, self::FINANCE_CREATE_PAYMENT, self::FINANCE_CREATE_EXPENSE,
+            self::FINANCE_VIEW_OVERVIEW, self::FINANCE_VIEW_INTERNAL_MARGIN, self::FINANCE_CREATE_PAYMENT, self::FINANCE_CREATE_EXPENSE,
             self::SALARIES_VIEW_OWN,
             self::INVENTORY_VIEW, self::INVENTORY_CREATE_PART, self::INVENTORY_EDIT_PART,
             self::INVENTORY_ADJUST_STOCK, self::INVENTORY_CREATE_PURCHASE, self::INVENTORY_RECEIVE_GOODS,