fix(audio-cpp): forward voice reference transcripts (#11997)

Saved voices send ref_text, but Fish Audio requires reference_text.
Derive the canonical parameter while preserving explicit overrides.
Both TTS modes use the shared builder.

Add regression cases and document the parameter alias.

Assisted-by: Codex:gpt-6

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: localai-org-maint-bot <306269227+localai-org-maint-bot@users.noreply.github.com>

docs/content/features/audio-cpp.md

@@ -233,6 +233,12 @@ voice conversion from the same weights.
 
 ## Family notes
 
+- **Fish Audio voice cloning**: save a reference clip with its transcript in the
+  Voice Library, then select **Use in Text to Speech**. The backend accepts
+  `params.ref_text` as an alias for `params.reference_text` in both ordinary and
+  streaming speech requests. If you supply both parameters, `reference_text`
+  takes precedence. For direct requests with a reference file in `voice`, supply
+  its transcript in one of these parameters.
 - **Supertonic**: use the `orig` GGUF package, whose weights are f32. The f16 package was
   observed to reach `ggml_concat` with mismatched operand types and take the backend
   process down with `SIGABRT` on the first request, rather than returning an error.