Port expressive mode example cleanup

[rosetta-livekit-bot]

Summary

No code changes are required for parity with livekit/agents#6370 because agents-js does not expose expressive mode, expressive presets, or expressive example configuration.

Verification

• pnpm build
• pnpm lint (completed successfully; existing warnings were reported)
• Package tests: not run because no package files were changed

Source diff coverage

Source file	Classification
examples/drive-thru/agent.py	Not applicable: target counterpart examples/src/drive-thru/drivethru_agent.ts does not import or configure expressive mode.
examples/frontdesk/agent.py	Not applicable: target counterpart examples/src/frontdesk/frontdesk_agent.ts does not import or configure expressive mode.
examples/healthcare/agent.py	Not applicable: no healthcare example counterpart exists in agents-js.
examples/inference/agent.py	Not applicable: no inference example counterpart exists in agents-js.
examples/survey/agent.py	Not applicable: target counterpart examples/src/survey_agent.ts does not import or configure expressive mode.
livekit-agents/livekit/agents/voice/__init__.py	Not applicable: target public barrel agents/src/voice/index.ts does not export expressive options or presets.
livekit-agents/livekit/agents/voice/agent.py	Not applicable: target agents/src/voice/agent.ts has no expressive agent option or getter.
livekit-agents/livekit/agents/voice/agent_activity.py	Not applicable: target agents/src/voice/agent_activity.ts has no expressive resolution or TTS markup injection path.
livekit-agents/livekit/agents/voice/agent_session.py	Not applicable: target agents/src/voice/agent_session.ts has no expressive session option or internal expressive state.
livekit-agents/livekit/agents/voice/presets.py	Not applicable: target has no voice/presets module or expressive preset API.

---

Ported from livekit/agents#6370

Original PR description

Remove the user-facing expressive surface while keeping the pipeline machinery internal and disabled:

• drop the expressive param from AgentSession and Agent (and the Agent.expressive property)
• drop the expressive field from AgentSessionOptions
• stop exporting ExpressiveOptions and presets from livekit.agents.voice
• AgentSession hardcodes an internal _expressive = False, which AgentActivity._resolve_expressive_options() now reads, so the markup/presets machinery stays intact but always resolves disabled
• remove expressive=presets.* usage from the examples

[changeset-bot]

⚠️ No Changeset found

Latest commit: 9327f84

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.