libomtd defines the output-side companion boundary for llama.cpp tools.

• libmtmd: input media -> model-readable embeddings/tokens
• libomtd: model output -> generated media

This patch only adds the OMTD framework and public API. Concrete output models and frontend wiring are added by follow-up patches.

OMTD is intended to be used from the same user-facing tools that already host model interaction:

llama-cli     --omtd FILE -> generated output file
llama-server  --omtd FILE -> generated output endpoint or stream
llama-tts     --omtd FILE -> generated speech/audio file

The framework-only patch does not add those flags yet. It adds the common library target and API first, so the later frontend patch can route all three frontends through the same OMTD boundary without introducing a model-specific backend at the same time.

A clean review sequence is:

1. OMTD core library and API
2. llama-cli / llama-server / llama-tts frontend wiring
3. First concrete OMTD backend

This keeps the generic OMTD design separate from any one output model.

OMTD is for generated outputs. It does not replace MTMD and it does not load --mmproj files.

Use:

• --mmproj FILE for MTMD input-media projectors
• --omtd FILE for OMTD output-media companions, once a frontend/backend patch wires a concrete output model to this API

The public C API is declared in omtd.h.

Detection helpers:

• omtd_is_output_companion_gguf(path)
• omtd_get_model_type(path)
• omtd_get_model_modality(path)

Generation entry point:

• omtd_audio_generate_file(params, error, error_size)

The framework patch returns OMTD_STATUS_UNSUPPORTED for audio generation until an audio backend is registered by a model-specific patch.

MTMD prepares input media so a language model can consume it. OMTD provides the library boundary for media generated from model output.