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.

PROJECT.md

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+# tuimble
+
+## Purpose
+
+A terminal-based Mumble client with full voice support. Fills the gap
+between heavyweight GUI clients and no-client-at-all for terminal users.
+
+## Success Criteria
+
+- Connect to any standard Mumble server
+- Transmit and receive voice audio
+- Push-to-talk with sub-100ms latency
+- Browse channels, see users, send/receive text
+- Works in Kitty, WezTerm, Ghostty, foot; degrades gracefully elsewhere
+
+## Constraints
+
+- Python 3.11+ (async features, tomllib)
+- Minimal dependencies (5 core libraries)
+- Single-user, single-server (no multi-server)
+- Linux-first (evdev fallback is Linux-only)
+
+## Non-Goals
+
+- GUI or web interface
+- Server administration
+- Audio recording/playback to file
+- Plugin system