feat: Add Elixir SDK Mix project configuration with HTTP/WebSocket dependencies and package metadata

- Add TelecomSDK.MixProject with app :telecom_sdk version 1.0.0 and Elixir ~> 1.15 requirement
- Add application config with :logger in extra_applications
- Add dependencies: finch ~> 0.16 for HTTP client, jason ~> 1.4 for JSON, websockex ~> 0.4 for WebSocket, ex_doc ~> 0.27 (dev only)
- Add package metadata with MIT license and GitHub repository link
- Set start_permanent based on Mix.env() == :prod

sdk/elixir/mix.exs

@@ -0,0 +1,39 @@
+defmodule TelecomSDK.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :telecom_sdk,
+      version: "1.0.0",
+      elixir: "~> 1.15",
+      start_permanent: Mix.env() == :prod,
+      deps: deps(),
+      description: "Elixir SDK for Telecom Platform",
+      package: package()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps.get" to learn about dependencies.
+  defp deps do
+    [
+      {:finch, "~> 0.16"},
+      {:jason, "~> 1.4"},
+      {:websockex, "~> 0.4"},
+      {:ex_doc, "~> 0.27", only: :dev, runtime: false}
+    ]
+  end
+
+  defp package do
+    [
+      licenses: ["MIT"],
+      links: %{"GitHub" => "https://github.com/nutcas3/telecom-platform"}
+    ]
+  end
+end