feat: scaffold tuimble TUI mumble client

Core modules: TUI app (textual), mumble protocol client,
audio pipeline (sounddevice + opus), push-to-talk with
kitty protocol / evdev / toggle backends. Config via TOML.

tests/test_config.py

@@ -0,0 +1,23 @@
+"""Tests for configuration module."""
+
+from tuimble.config import Config, PttConfig, ServerConfig
+
+
+def test_default_config():
+    cfg = Config()
+    assert cfg.server.host == "localhost"
+    assert cfg.server.port == 64738
+    assert cfg.audio.sample_rate == 48000
+    assert cfg.ptt.mode == "hold"
+
+
+def test_server_config():
+    srv = ServerConfig(host="mumble.example.com", port=12345)
+    assert srv.host == "mumble.example.com"
+    assert srv.port == 12345
+
+
+def test_ptt_config_defaults():
+    ptt = PttConfig()
+    assert ptt.key == "space"
+    assert ptt.backend == "auto"