feat: salvage Angular developer skill

skills/angular-developer/references/defining-providers.md

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+# Defining Dependency Providers
+
+Angular offers automatic and manual ways to provide dependencies to its Dependency Injection (DI) system.
+
+## Automatic Provision
+
+The most common way to provide a service is using `providedIn: 'root'` on an `@Injectable()`.
+
+### InjectionToken
+
+Use `InjectionToken` for non-class dependencies (configuration objects, functions, primitives). An `InjectionToken` can also be automatically provided.
+
+```ts
+import {InjectionToken} from '@angular/core';
+
+export interface AppConfig {
+  apiUrl: string;
+}
+
+export const APP_CONFIG = new InjectionToken<AppConfig>('app.config', {
+  providedIn: 'root',
+  factory: () => ({apiUrl: 'https://api.example.com'}),
+});
+```
+
+## Manual Provision
+
+You use the `providers` array when a service lacks `providedIn`, when you want a new instance for a specific component, or when configuring runtime values.
+
+```ts
+@Component({
+  providers: [
+    // Shorthand for { provide: LocalService, useClass: LocalService }
+    LocalService,
+
+    // useClass: Swap implementations
+    {provide: Logger, useClass: BetterLogger},
+
+    // useValue: Provide static values
+    {provide: API_URL_TOKEN, useValue: 'https://api.example.com'},
+
+    // useFactory: Generate value dynamically
+    {
+      provide: ApiClient,
+      useFactory: (http = inject(HttpClient)) => new ApiClient(http),
+    },
+
+    // useExisting: Create an alias
+    {provide: OldLogger, useExisting: NewLogger},
+
+    // multi: Provide multiple values for the same token as an array
+    {provide: INTERCEPTOR_TOKEN, useClass: AuthInterceptor, multi: true},
+  ],
+})
+export class Example {}
+```
+
+## Scopes of Providers
+
+- **Application Bootstrap**: Global singletons. Use for HTTP clients, logging, or app-wide config.
+- **Component/Directive**: Isolated instances. Use for component-specific state or forms. Services are destroyed when the component is destroyed.
+- **Route**: Feature-specific services loaded only with specific routes.
+
+## Library Pattern: `provide*` functions
+
+Library authors should export functions that return provider arrays to encapsulate configuration:
+
+```ts
+export function provideAnalytics(config: AnalyticsConfig): Provider[] {
+  return [{provide: ANALYTICS_CONFIG, useValue: config}, AnalyticsService];
+}
+```