audio: splice full transcript; reject oversized requests via context

[barvhaim]

…check (#45)

The audio cascade truncated the transcript to a context-derived per-clip budget (asr_generation_reserve_tokens held back for the answer). When that reserve met or exceeded the served max_model_len, the budget floored to 1 token: the model saw no question and refused, with no error (#45).

Rather than patch the truncation math, remove it. The transcript is now spliced into the prompt in full, as ordinary text tokens. A request whose prompt + transcript(s) can't leave room for the answer within max_model_len is rejected by vLLM's standard prompt-length check (HTTP 400) — the same loud failure text-only requests already get, instead of a silent 1-token transcript. This also makes audio behave identically to long text.

Details:

• Remove asr_generation_reserve_tokens entirely (config field + validation, compose CLI flag, processor accessor). It only existed to size the old truncation budget.
• Drop the budget param / ids[:budget] truncation in the processor; splice the full transcript.
• get_mm_max_tokens_per_item now reports max(1, seq_len // count) — the honest worst-case transcript positions one clip can occupy. This still sizes vLLM's encoder cache correctly (embed_multimodal emits one row per transcript token); it is a profiling hint, not a request bound.
• Remove the now-dead audio_token_budget helper and its tests.

Tests updated; docs/AUDIO.md rewritten to describe reject-not-truncate.