docs: deprecate "Skill" in allowed_tools in favor of skills option

[qing-ant]

Summary

Adds a deprecation note in src/claude_agent_sdk/types.py documenting that passing "Skill" in allowed_tools (and in AgentDefinition.tools) is deprecated. Users should use the skills option on ClaudeAgentOptions instead, which provides more granular control over which skills are available.

This is a docs-only change — no behavior changes.

🤖 Generated with Claude Code

[claude]

LGTM — docs-only deprecation notes, no behavior change.

Extended reasoning...

Overview

This PR adds two documentation-only changes to src/claude_agent_sdk/types.py: an inline comment on AgentDefinition.tools and a .. deprecated:: block in the ClaudeAgentOptions.allowed_tools docstring, both noting that passing "Skill" is deprecated in favor of the skills option. No code paths, type signatures, defaults, or runtime behavior are touched.

Security risks

None. The change consists entirely of comments and docstrings; there is no executable code, no input handling, and no auth/permissions logic affected.

Level of scrutiny

Low. This is a mechanical docs update that aligns with the already-documented behavior of the skills option (whose existing docstring already states that setting it auto-configures the Skill tool and that adding "Skill" to allowed_tools is unnecessary). The deprecation notes are consistent with that.

Other factors

No bugs were found by the bug hunting system, there are no outstanding reviewer comments, and the diff is small and self-contained. The reST .. deprecated:: directive is well-formed and the inline comment placement is conventional.