[A365 support] Add Agent 365 token support

[heyitsaamir]

Adds Agent 365 agent user token support to TokenManager.

Why:
This lets apps request resource tokens for an agent identity acting through its agent user, including Teams bot API tokens.

Interesting bits:

• Added generic get_agent_user_token(scope=...) plus get_agent_bot_token() convenience.
• Uses MSAL's user FIC support and a client assertion callback for T1 so we don't sit on stale assertions.
• Added an agent365 example that reads values from env vars and avoids printing the full token. tiny safety win.

Reviewer tips:
Start with packages/apps/src/microsoft_teams/apps/token_manager.py, then examples/agent365/src/main.py.

Testing:

• uv run pytest packages/apps/tests/test_token_manager.py
• uv run ruff check packages/apps/src/microsoft_teams/apps/token_manager.py examples/agent365/src/main.py stubs/msal/init.pyi
• pre-commit hooks on commit: ruff, ruff format, pyright, license header

[heyitsaamir]

This change is part of the following stack:

• Agent 365 support #464
  • [A365 support] Add Agent 365 token support #457 ◀
    • Support Entra inbound Agent ID tokens #462
      • Add AgenticIdentity API surface #478
        • Remove ActivitySender send abstraction #479
          • Add app-level agentic send helpers #480

_{Change managed by git-spice.}