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.

TASKLIST.md

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+# Task List
+
+## Active
+
+- [ ] Wire TUI to MumbleClient (connect on startup, display state)
+- [ ] Implement text message send/receive in chat log
+
+## Pending
+
+- [ ] Audio pipeline integration with MumbleClient
+- [ ] PTT wiring (key events -> audio.capturing toggle)
+- [ ] Channel tree population from server data