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.

composer.json

@@ -53,7 +53,7 @@
             "Modules\\": "Modules/"
         },
         "files": [
-            "app/Space/helpers.php"
+            "app/Support/helpers.php"
         ]
     },
     "autoload-dev": {