Master data review: spec updates and C1/C2/M3-M6 fixes

Spec (docs/reviewing/master-data.md):
- M1: Remove margin from stored product fields (it's a derived frontend value)
- M2: Clarify posting window only restricts transaction dates, not master data
- M5: Document AccountFormulaManager::delete() as archive, not physical delete

Code:
- C1: Fix CompanySettingManager property typo (company_id → companyId) —
  prevented PHP 8.4 dynamic property fatal on all posting window operations
- C2: Fix WarehouseManager::deleteWarehouse() guard — was comparing
  warehouse_name (string) against warehouse id column (no-op); now correctly
  blocks on storage rows and active stock rows
- M3: Remove hard-delete of td_rack_log in deleteStorage() — retain rack
  history consistent with soft-delete philosophy elsewhere
- M4: Add reference guards to ChartOfAccounts::delete() (blocks on GL items,
  formula items, product account mappings) and DepartmentManager::delete()
  (blocks on GL items)
- M6: Fix CompanySettingManager::handle() partial update — only upsert keys
  present in the request, not all allowed keys defaulted

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

app/assets/utils/classes/CompanySettingManager.php

@@ -19,7 +19,7 @@ class CompanySettingManager
 {
     private PDO $pdo;
     private ?PDO $transactionPdo;
-    private int $company_id;
+    private int $companyId;
 
     // ── Known keys with their defaults ───────────────────────────────────────
     private const DEFAULTS = [
@@ -316,7 +316,9 @@ class CompanySettingManager
             $allowed = array_keys(self::DEFAULTS);
             $incoming = [];
             foreach ($allowed as $key) {
-                $incoming[$key] = $data[$key] ?? self::DEFAULTS[$key];
+                if (array_key_exists($key, $data)) {
+                    $incoming[$key] = $data[$key];
+                }
             }
 
             $blocked = $this->blockedChanges($incoming);