feat(elevenlabs): add new models [bot]

[hganwani-droid]

Auto-generated by model-addition-agent for provider elevenlabs.

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Note

Low Risk
Low-risk data-only change adding two new ElevenLabs model definition YAMLs. Main risk is if mode: unknown is rejected by validation or causes these models to be unusable until a supported mode is set.

Overview
Adds two new ElevenLabs provider model definition files, eleven_english_sts_v2.yaml and eleven_multilingual_sts_v2.yaml, registering the corresponding model IDs.

Both configs currently set mode: unknown, differing from existing ElevenLabs entries that specify a concrete mode.

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