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.

docs/DEBUG.md

@@ -0,0 +1,45 @@
+# Debugging
+
+## Verbose Mode
+
+```sh
+tuimble --verbose                # (planned)
+```
+
+## Common Issues
+
+### No audio devices found
+
+```sh
+python3 -c "import sounddevice; print(sounddevice.query_devices())"
+```
+
+Check that portaudio is installed and devices are accessible.
+
+### opuslib import error
+
+```sh
+python3 -c "import opuslib"
+```
+
+If this fails, install libopus: `apt install libopus0`
+
+### Kitty protocol not detected
+
+Verify terminal supports the Kitty keyboard protocol.
+Known working: Kitty, WezTerm, Ghostty, foot.
+
+### evdev permission denied
+
+```sh
+ls -la /dev/input/event*
+groups                           # should include 'input'
+```
+
+Add user to `input` group: `sudo usermod -aG input $USER`
+
+### Connection refused
+
+- Verify server address and port
+- Check firewall allows outbound TCP/UDP to port 64738
+- Test with: `nc -zv <host> 64738`