add HumeAI TADA TTS engine (1B English + 3B Multilingual)

Integrates HumeAI's TADA (Text-Acoustic Dual Alignment) speech-language
model as a new TTS engine. TADA uses a novel 1:1 token-audio alignment
that produces coherent speech over long sequences (700s+).

Two model variants:
- tada-1b: English-only, ~4GB, built on Llama 3.2 1B
- tada-3b-ml: 10 languages, ~8GB, built on Llama 3.2 3B

Backend uses the Encoder for voice prompt encoding with caching, and
TadaForCausalLM with flow-matching diffusion for generation. Supports
bf16 inference on CUDA, forces CPU on macOS (MPS compatibility).

Installed with --no-deps due to torch>=2.7 pin conflict; descript-audio-codec
and torchaudio added as explicit sub-dependencies.

justfile

@@ -46,6 +46,8 @@ setup-python:
     {{ pip }} install -r {{ backend_dir }}/requirements.txt
     # Chatterbox pins numpy<1.26 / torch==2.6 which break on Python 3.12+
     {{ pip }} install --no-deps chatterbox-tts
+    # HumeAI TADA pins torch>=2.7,<2.8 which conflicts with our torch>=2.1
+    {{ pip }} install --no-deps hume-tada
     # Apple Silicon: install MLX backend
     if [ "$(uname -m)" = "arm64" ] && [ "$(uname)" = "Darwin" ]; then
         echo "Detected Apple Silicon — installing MLX dependencies..."
@@ -74,6 +76,7 @@ setup-python:
     }
     & "{{ pip }}" install -r {{ backend_dir }}/requirements.txt
     & "{{ pip }}" install --no-deps chatterbox-tts
+    & "{{ pip }}" install --no-deps hume-tada
     & "{{ pip }}" install git+https://github.com/QwenLM/Qwen3-TTS.git
     & "{{ pip }}" install pyinstaller ruff pytest pytest-asyncio -q
     Write-Host "Python environment ready."