[Feature]: Add AgentScope 2.0 usage examples

**Is your feature request related to a problem? Please describe.**
Current samples mostly cover v1.x. There is a lack of runnable examples for v2.0 core features (Workspace backends, Team, AgentService, WebUI), making it hard for new users to get started.

**Describe the solution you'd like**
Add a v2/directory with minimal demos:
Workspace: Switching between Local/Docker/OpenSandbox.
Team: Basic leader-worker interaction.
AgentService: Starting the service and chatting via WebUI/API.
WebUI: Demos for fork session and deferred send.

**Describe alternatives you've considered**
Expanding the main repo docs, but code examples are better suited for this repo.