refactor(services): Documents→Document + ExchangeRate→Integrations/ExchangeRate

Two follow-ups to the Services reorg that landed in 6d1816bd.

**Documents → Document** (singular). Documents/ was the only plural subdir in app/Services/ — every other bucket (Company, Mail, Module, Pdf, Storage, Update, ExchangeRate) was singular. Renaming to Document/ normalizes the whole tree.

**ExchangeRate → Integrations/ExchangeRate**. Introduces Integrations/ as an umbrella for external-service adapter subsystems. Exchange rate providers move in first; AI providers, payment gateways, and any other driver-pattern integrations land as sibling subdirs (Integrations/Ai/, Integrations/Payment/) without another reorg. Integrations/ was chosen over Providers/ to avoid conceptual collision with Laravel's app/Providers/ — 'check the providers' shouldn't be ambiguous.

17 files moved, 21 consumer files rewritten to point at the new namespaces via literal-string replacement (same approach as the previous reorg). 350 tests pass, Pint clean.

app/Services/Integrations/ExchangeRate/ExchangeRateDriver.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace App\Services\Integrations\ExchangeRate;
+
+abstract class ExchangeRateDriver
+{
+    public function __construct(
+        protected string $apiKey,
+        protected array $config = [],
+    ) {}
+
+    /**
+     * Fetch exchange rate between two currencies.
+     *
+     * @return array Exchange rate values
+     */
+    abstract public function getExchangeRate(string $baseCurrency, string $targetCurrency): array;
+
+    /**
+     * Get list of currencies supported by this provider.
+     *
+     * @return array Currency codes
+     */
+    abstract public function getSupportedCurrencies(): array;
+
+    /**
+     * Validate that the API key and connection work.
+     *
+     * @return array Exchange rate values (proof of working connection)
+     *
+     * @throws ExchangeRateException
+     */
+    abstract public function validateConnection(): array;
+}