chore: upgrade agora-agents to 2.9.0 and client toolkit to 2.10.0

[a282993047]

What

Upgrade this quickstart to agora-agents 2.9.0 and Agent Client Toolkit 2.10.0, including the Toolkit initialization API migration.

Changes

• Raise the Python SDK minimum from >=2.3.0 to >=2.9.0, preserving the existing minimum-version policy.
• Upgrade the web Toolkit from 1.2.0 to 2.10.0 and refresh the Bun lockfile.
• Pass rtmEngine directly to AgoraVoiceAI.init, replacing nested rtmConfig.
• Add Bun type definitions and narrow the stub server's optional port before constructing the proxy verification URL.
• Update setup, architecture, session lifecycle, and migration documentation.

Verification

• Passed 14 backend tests and 6 frontend tests.
• Passed web TypeScript, API contract, production build, and local proxy/FastAPI smoke checks using the repository's Bun workflow.
• Passed git diff --check.
• The tester confirmed a successful live call locally.

Known limitation: UIKit 1.1.0 still declares an optional Toolkit peer dependency of ^1.2.0; the mismatch with Toolkit 2.10.0 is documented. A successful local call does not establish exhaustive transcript, metrics, interruption, or teardown coverage.