[codex] Clarify Python SDK skill invocation

[RezinChow]

Summary

Clarifies the Python SDK path for folder-style skills and direct skill invocation.

• document skill_dirs, search_skills, and Skill usage in the Python SDK README
• add a concise Skills section to the Python quick reference
• update the skill-tool example from obsolete await session.send(...) usage to the current synchronous API
• fix one Python binding docstring that still showed await session.send(...)

Why

The SDK already supports loading folder-style skills through skill_dirs and invoking them with session.tool("Skill", {...}), but the Python-facing docs did not show that path clearly. The old example also mixed in async-style usage that does not match the current PyO3 API.

Validation

• git diff --check origin/main..HEAD
• python3 -m py_compile examples/test_skill_tool.py

Rust checks were not run locally because cargo is not installed in this environment.

[ZhiXiao-Lin]

I took a look at this PR:

• mergeable_state is clean, so there are no merge conflicts.
• Both check runs have passed: Check and SDK build check.
• The diff is small and mostly updates the Python SDK skill invocation docs/examples. I do not see a blocking issue in the changes.

The only thing to resolve before merging is that this PR is still marked as Draft. GitHub will not allow a Draft PR to be merged, so please mark it as Ready for review first; after that, it should be good to merge according to the repo's normal process.

[ZhiXiao-Lin]

Rebased the contribution onto the current modular Python SDK while preserving the original author. The moved PySession example now updates sdk/python/src/session.rs; the current A3S-Lab release URL and newer dynamic-workflow docs were retained alongside the skill examples.

Validation:

• cargo fmt --all -- --check
• cargo check --manifest-path sdk/python/Cargo.toml
• python3 -m py_compile examples/test_skill_tool.py
• git diff --check

[ZhiXiao-Lin]

Reviewed the Python SDK examples and bindings. The examples now use the synchronous session.send() / session.tool() APIs correctly, SessionOptions is imported before use, and both supported skill-directory configuration paths are documented consistently. CI is green.

[ZhiXiao-Lin]

Revalidated after merging current main (v6.0.0) into the contribution. The only conflict was the Python SDK wheel-install example; the current 6.0.0 placeholder guidance was retained while preserving the PR's skill-discovery and synchronous API corrections.

Local validation passed: formatting, event-protocol artifacts, SDK API alignment, Python example syntax, and cargo check --manifest-path sdk/python/Cargo.toml. GitHub CI is now green for Check, SDK build check, and Windows check.