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.

ROADMAP.md

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+# Roadmap
+
+## Phase 1 — Foundation (current)
+
+- [x] Project scaffold
+- [ ] Basic TUI layout (channels, chat, status)
+- [ ] Mumble server connection
+- [ ] Text chat (send/receive)
+
+## Phase 2 — Voice
+
+- [ ] Audio pipeline (capture + playback)
+- [ ] Opus encode/decode integration
+- [ ] Push-to-talk (Kitty protocol)
+- [ ] PTT fallbacks (evdev, toggle)
+
+## Phase 3 — Polish
+
+- [ ] Channel tree navigation
+- [ ] User list with status indicators
+- [ ] Volume control
+- [ ] Server certificate handling
+- [ ] Config file hot-reload
+
+## Phase 4 — Robustness
+
+- [ ] Reconnection handling
+- [ ] Error recovery
+- [ ] Audio device hot-swap
+- [ ] Comprehensive test suite