feat(exchange-rate): make providers extendible via module Registry

Exchange rate providers are now pluggable via the module Registry. The four built-in drivers (currency_converter, currency_freak, currency_layer, open_exchange_rate) move from a static config array into App\\Providers\\DriverRegistryProvider, which calls Registry::registerExchangeRateDriver() for each during app boot with metadata the frontend needs: label (i18n key), website (help-text URL), and config_fields (schema for driver-specific driver_config JSON).

The Currency Converter's server-type selector and dedicated URL field — previously hardcoded in ExchangeRateProviderModal.vue — are now just another config_fields entry with a visible_when rule that shows the URL input only when type=DEDICATED. Any module that wants to ship a custom driver gets the same treatment for free: declare config_fields in the registration, and the host app's modal renders them automatically.

ExchangeRateDriverFactory::make() falls back to Registry::driverMeta() when a name isn't in the local built-in map, and availableDrivers() merges both sources. ConfigController handles the exchange_rate_drivers key specially by mapping Registry::allDrivers('exchange_rate') to enriched option objects, so the config-file route still works for every other key. The static exchange_rate_drivers + currency_converter_servers arrays in config/invoiceshelf.php are deleted.

Unit tests cover the new Registry::register/flushDrivers, the factory merging built-ins with Registry-contributed drivers, and the factory rejecting unknown names. A feature test exercises the end-to-end /api/v1/config?key=exchange_rate_drivers response shape.

NOTE: this commit depends on invoiceshelf/modules package commit e44d951 which adds the Registry driver API. The package needs to be released and pinned in composer.json before a fresh composer install on this commit will work.

resources/scripts/api/services/exchange-rate.service.ts

@@ -40,17 +40,29 @@ export interface BulkUpdatePayload {
   }>
 }
 
-export interface ConfigOption {
-  key: string
+export interface DriverConfigFieldOption {
+  label: string
   value: string
 }
 
-export interface ConfigDriversResponse {
-  exchange_rate_drivers: ConfigOption[]
+export interface DriverConfigField {
+  key: string
+  type: 'text' | 'select'
+  label: string
+  options?: DriverConfigFieldOption[]
+  default?: string
+  visible_when?: Record<string, string>
 }
 
-export interface ConfigServersResponse {
-  currency_converter_servers: ConfigOption[]
+export interface ExchangeRateDriverOption {
+  value: string
+  label: string
+  website?: string
+  config_fields?: DriverConfigField[]
+}
+
+export interface ConfigDriversResponse {
+  exchange_rate_drivers: ExchangeRateDriverOption[]
 }
 
 export interface SupportedCurrenciesParams {
@@ -133,15 +145,12 @@ export const exchangeRateService = {
   },
 
   // Config
-  // Backend returns { exchange_rate_drivers: Array<{ key, value }> }
+  // Backend returns { exchange_rate_drivers: ExchangeRateDriverOption[] } where each option
+  // includes the metadata needed to render a driver-specific config form (label, website,
+  // config_fields). The list is built dynamically from the module Registry, so module-
+  // contributed drivers appear here automatically.
   async getDrivers(): Promise<ConfigDriversResponse> {
     const { data } = await client.get(API.CONFIG, { params: { key: 'exchange_rate_drivers' } })
     return data
   },
-
-  // Backend returns { currency_converter_servers: Array<{ key, value }> }
-  async getCurrencyConverterServers(): Promise<ConfigServersResponse> {
-    const { data } = await client.get(API.CONFIG, { params: { key: 'currency_converter_servers' } })
-    return data
-  },
 }