gateway: bill Tinfoil's per-request charges on the audio paths

Tinfoil bills voxtral-tts $0.002 and whisper-large-v3-turbo $0.01 per REQUEST,
with $0 per token for both. Reading only the two token prices in its model list
made TTS look free and left STT billed at an older catalog's $0.05/1M tokens, so
neither matched what the co-op actually pays.

LiteLLM cannot express a per-request charge on the audio paths: per-request
pricing exists only on the search/rerank/MCP paths via input_cost_per_query, and
input_cost_per_request is read only by the proxy's cost-tracking settings, never
by the model cost calculator.

So patch_audio_request_cost.py, a build-time patch in the same shape as
patch_image_cost.py, makes response_cost_calculator honour a declared
input_cost_per_request. That function is the single funnel for every call type —
the proxy dispatches audio as `aspeech` and `transcription` and reaches it
through Logging._response_cost_calculator — so one insertion covers both. The
charge resolves from the per-deployment custom_pricing the logging layer builds
from our model_info, then the shared cost map, then call metadata, and the patch
is inert for any model that declares nothing.

config.yaml declares the real charges: $0.002/request for voxtral-tts, and
$0.01/request for whisper with its token price corrected to $0.

Verified before committing: the patch applies to the installed 1.103.2 anchors
and compiles; the helper's resolution order passes unit checks (all branches,
plus inert and garbage cases); the resulting config validates as YAML with all
12 entries intact. End-to-end spend is proven after deploy by a real TTS/STT call.

Refs code/litellm#5

README.md

@@ -158,6 +158,7 @@ expect a 15–20 min maintenance window and **never panic-restart mid-migration*
 
 - Check the [LiteLLM changelog](https://github.com/BerriAI/litellm/releases) for breaking changes
 - The `start.sh` and `config.yaml` may need adjustment if LiteLLM changes its env-var or config schema
+- **Build-time patches ride on LiteLLM internals — verify each one after an upgrade.** `patch_budget_message.py`, `patch_image_cost.py` (keeps image-gen pricing on the shared cost-map key) and `patch_audio_request_cost.py` (adds the declared per-request charge on the audio paths: Tinfoil bills `voxtral-tts` $0.002 and `whisper-large-v3-turbo` $0.01 per request, which the cost map cannot express). Each prints `[coop-patch]` in the build log. They are non-fatal by design: a missing anchor warns and the build still succeeds, so the behaviour can vanish silently on a version bump. Related: code/litellm#5.
 - The CORS env var is `LITELLM_CORS_ORIGINS` (upstream-native since 1.84.0); the old `LITELLM_CORS_ALLOWED_ORIGINS` + sed patch are dead — don't re-add them
 - Test on a staging instance if the version jump is large