fix: accept skill alias in skill tool

[Bortlesboat]

Summary

• accept skill as an alias for name in the skill_manage input payload
• expose the alias in the tool schema so the external Skill(...) wrapper shape is handled explicitly
• add regression coverage for Skill(skill=...) routing to the requested skill name instead of the missing-name error

Verification

• RED: cargo test -p jcode test_load_accepts_skill_alias --lib failed before the fix with the expected missing-name path
• GREEN: cargo test -p jcode test_load_accepts_skill_alias --lib
• cargo test -p jcode tool::skill::tests --lib
• cargo check -p jcode
• cargo fmt --check
• git diff --check -- src/tool/skill.rs

Closes #165

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