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_ptt.py

@@ -0,0 +1,37 @@
+"""Tests for push-to-talk backends."""
+
+from tuimble.ptt import KittyPtt, PttState, TogglePtt
+
+
+def test_kitty_ptt_press_release():
+    states = []
+    ptt = KittyPtt(lambda tx: states.append(tx))
+    assert ptt.state is PttState.IDLE
+
+    ptt.key_down()
+    assert ptt.state is PttState.TRANSMITTING
+    assert states == [True]
+
+    ptt.key_up()
+    assert ptt.state is PttState.IDLE
+    assert states == [True, False]
+
+
+def test_kitty_ptt_no_duplicate_events():
+    states = []
+    ptt = KittyPtt(lambda tx: states.append(tx))
+
+    ptt.key_down()
+    ptt.key_down()  # repeat, no state change
+    assert states == [True]
+
+
+def test_toggle_ptt():
+    states = []
+    ptt = TogglePtt(lambda tx: states.append(tx))
+
+    ptt.toggle()
+    assert ptt.transmitting is True
+    ptt.toggle()
+    assert ptt.transmitting is False
+    assert states == [True, False]