feat(cli): add --no-user-skills toggle wired to AgentContext

[antznette1]

This PR adds a --no-user-skills CLI flag and wires it through to the agent runtime.

What it does

• Adds --no-user-skills to create_main_parser, with user_skills defaulting to True:

  • Default: load user skills.
  • --no-user-skills: user_skills=False.

• Threads the flag end-to-end:

  • simple_main.main() → agent_chat.run_cli_entry(user_skills=args.user_skills)
  • run_cli_entry(...) → verify_agent_exists_or_setup_agent(user_skills=...)
    and setup_conversation(..., user_skills=...)
  • setup.load_agent_specs(..., user_skills=...) → AgentStore.load(..., load_user_skills=user_skills)

• Updates AgentStore.load(...) to:

  • Accept load_user_skills: bool = True

  • Pass it into AgentContext(..., load_user_skills=load_user_skills)

  • Fallback on older SDKs that don’t accept this kwarg:

    try:
        agent_context = AgentContext(..., load_user_skills=load_user_skills)
    except TypeError:
        agent_context = AgentContext(...)

Notes

• I tested locally on Windows; some tests fail with fcntl / NoConsoleScreenBufferError, which are not specific to this change. CI on Linux/macOS should not hit those.
• I kept this PR intentionally focused: no Windows-specific hacks or unrelated refactors, just the flag wiring and compatibility guard.