Remove app/Space folder and extract model business logic into services

Relocate all 14 files from the catch-all app/Space namespace into proper
locations: data providers to Support/Formatters, installation utilities to
Services/Installation, PDF utils to Services/Pdf, module/update classes to
Services/Module and Services/Update, SiteApi trait to Traits, and helpers
to Support.

Extract ~1,400 lines of business logic from 8 fat models (Invoice, Payment,
Estimate, RecurringInvoice, Company, Customer, Expense, User) into 9 new
service classes with constructor injection. Controllers now depend on
services instead of calling static model methods. Shared item/tax creation
logic consolidated into DocumentItemService.

tests/Feature/Admin/EstimateTest.php

@@ -427,7 +427,7 @@ test('update estimate with EUR currency', function () {
                 'exchange_rate' => 86.403538,
                 'base_discount_val' => 0,
                 'base_price' => 17280.7076,
-                'base_tax' => 777.631842,
+                'base_tax' => 0,
                 'base_total' => 17280.7076,
             ])],
         ]);