fix(voice): align session.say transcripts with TTS

[swayamg20]

Summary

• use TTS-provided timed transcripts for session.say() when aligned transcripts are enabled and supported
• preserve raw scripted text when alignment is disabled, unsupported, bypassed by caller-provided audio, or audio output is disabled
• add regression coverage for the aligned path and each direct fallback path

Fixes #2067

Testing

• pnpm test agents/src/voice/agent_activity_say_aligned_transcript.test.ts agents/src/voice/agent_activity_close_commit.test.ts agents/src/voice/agent_activity_interrupted_commit.test.ts agents/src/voice/generation_tts_timeout.test.ts --silent (20 passed)
• pnpm test agents/src --exclude agents/src/voice/remote_session.test.ts --silent (1,561 passed, 5 skipped; the excluded file has an unrelated current-main event assertion mismatch)
• pnpm build:agents
• pnpm format:check
• targeted ESLint for the changed voice files
• pnpm exec changeset status --since=origin/main

[changeset-bot]

🦋 Changeset detected

Latest commit: 5e0fee0

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 39 packages

Name	Type
@livekit/agents	Patch
@livekit/agents-plugin-anam	Patch
@livekit/agents-plugin-anthropic	Patch
@livekit/agents-plugin-assemblyai	Patch
@livekit/agents-plugin-azure	Patch
@livekit/agents-plugin-baseten	Patch
@livekit/agents-plugin-bey	Patch
@livekit/agents-plugin-cartesia	Patch
@livekit/agents-plugin-cerebras	Patch
@livekit/agents-plugin-deepgram	Patch
@livekit/agents-plugin-did	Patch
@livekit/agents-plugin-elevenlabs	Patch
@livekit/agents-plugin-fishaudio	Patch
@livekit/agents-plugin-google	Patch
@livekit/agents-plugin-hedra	Patch
@livekit/agents-plugin-hume	Patch
@livekit/agents-plugin-inworld	Patch
@livekit/agents-plugin-krisp	Patch
@livekit/agents-plugin-lemonslice	Patch
@livekit/agents-plugin-liveavatar	Patch
@livekit/agents-plugin-livekit	Patch
@livekit/agents-plugin-minimax	Patch
@livekit/agents-plugin-mistral	Patch
@livekit/agents-plugin-mistralai	Patch
@livekit/agents-plugin-neuphonic	Patch
@livekit/agents-plugin-openai	Patch
@livekit/agents-plugin-perplexity	Patch
@livekit/agents-plugin-phonic	Patch
@livekit/agents-plugin-protoface	Patch
@livekit/agents-plugin-resemble	Patch
@livekit/agents-plugin-rime	Patch
@livekit/agents-plugin-runway	Patch
@livekit/agents-plugin-sarvam	Patch
@livekit/agents-plugin-silero	Patch
@livekit/agents-plugin-soniox	Patch
@livekit/agents-plugin-tavus	Patch
@livekit/agents-plugins-test	Patch
@livekit/agents-plugin-trugen	Patch
@livekit/agents-plugin-xai	Patch

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