Add .env support for transport and sound device configuration

- Add python-dotenv support to control_server.py and sound.py
- Load TRANSPORT from environment variable (default: spi)
- Load AUDIO_INPUT_DEVICE from environment variable (default: 7)
- Load all port configurations from environment variables
- Update .env.example with comprehensive configuration options
- Create .env file with sensible defaults for Pi
- Transport, sound device, and network settings now configurable via .env

Pipfile.lock

@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "3f3ca9af45dd4382aac3c649ae11cefbe97059ad14f40172735213c4919baada"
+            "sha256": "db66b0f2b4e51e5a0bc2edc0d89af123c03928c72add32c16ba955eaefc34da7"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -162,6 +162,14 @@
             "index": "pypi",
             "version": "==0.2.14"
         },
+        "python-dotenv": {
+            "hashes": [
+                "sha256:31f23644fe2602f88ff55e1f5c79ba497e01224ee7737937930c448e4d0e24dc",
+                "sha256:a8a6399716257f45be6a007360200409fce5cda2661e3dec71d23dc15f6189ab"
+            ],
+            "index": "pypi",
+            "version": "==1.1.1"
+        },
         "python-rtmidi": {
             "hashes": [
                 "sha256:052c89933cae4fca354012d8ca7248f4f9e1e3f062471409d48415a7f7d7e59e",