docs: Add Swift SDK README with comprehensive API documentation and implement authentication provider with JWT support

- Add README.md with installation instructions, architecture overview, and API examples for all SDK modules
- Add AuthProvider class with API key and JWT token support (generateJWTToken, validateJWTToken, getHeaders, clearTokenCache methods)
- Add HTTPClient base class with retry logic, error handling, and timeout management
- Add GraphQLAPI, PaymentAPI, RatingPlanAPI, SubscriberAPI, SystemAPI, and UsageAPI modules
- Add TelecomSDK main client integrating all API

sdk/swift/Sources/TelecomSDK/SubscriberAPI.swift

@@ -0,0 +1,56 @@
+import Foundation
+
+/// API for subscriber management
+public class SubscriberAPI {
+    private let client: HTTPClient
+    
+    public init(client: HTTPClient) {
+        self.client = client
+    }
+    
+    /// Get subscriber by ID
+    public func get(id: Int64) async throws -> Subscriber {
+        return try await client.get(path: "/v1/subscribers/\(id)")
+    }
+    
+    /// List subscribers with pagination
+    public func list(page: Int = 1, pageSize: Int = 50, status: SubscriberStatus? = nil) async throws -> SubscriberList {
+        var params: [String: String] = [
+            "page": "\(page)",
+            "page_size": "\(pageSize)"
+        ]
+        
+        if let status = status {
+            params["status"] = "\(status)"
+        }
+        
+        return try await client.get(path: "/v1/subscribers", params: params)
+    }
+    
+    /// Create a new subscriber
+    public func create(_ request: CreateSubscriberRequest) async throws -> Subscriber {
+        return try await client.post(path: "/v1/subscribers", body: request)
+    }
+    
+    /// Update an existing subscriber
+    public func update(id: Int64, request: UpdateSubscriberRequest) async throws -> Subscriber {
+        return try await client.put(path: "/v1/subscribers/\(id)", body: request)
+    }
+    
+    /// Delete a subscriber
+    public func delete(id: Int64) async throws {
+        try await client.delete(path: "/v1/subscribers/\(id)")
+    }
+    
+    /// Suspend a subscriber
+    public func suspend(id: Int64) async throws -> Subscriber {
+        return try await client.post(path: "/v1/subscribers/\(id)/suspend", body: nil as EmptyRequest?)
+    }
+    
+    /// Activate a suspended subscriber
+    public func activate(id: Int64) async throws -> Subscriber {
+        return try await client.post(path: "/v1/subscribers/\(id)/activate", body: nil as EmptyRequest?)
+    }
+}
+
+private struct EmptyRequest: Encodable {}