feat(cli): add read-only load_skill command

[RainLib]

Summary

• embed the bundled skills/ tree into the Rust binary at build time
• add the read-only load_skill, load_skill <name>, and load_skill <name> --path <relpath> surfaces from C#
• strip setup instructions from loaded entry files and append a compact reference manifest
• reject traversal and binary assets on the text channel without installing or writing files
• record CLI-003 as implemented in the durable C# parity ledger

Atomic scope

This PR only ports CLI-003 (load_skill). It is stacked on the schema CRC PR because both use the same build-time embedded-resource generator; the diff against its base contains no schema CRC behavior.

Validation

cargo fmt -- --check
cargo clippy --all-targets -- -D warnings
cargo test --workspace
cargo test -p officecli commands::load_skill::tests
cargo test -p officecli --test cli_smoke test_load_skill
target/debug/officecli help load_skill
target/debug/officecli load_skill morph-ppt --path reference/decision-rules.md

All passed locally. The tests cover the catalog, full front-matter descriptions, alias casing, setup-section removal, reference manifests, direct text reads, Windows separators, traversal rejection, binary rejection, unknown skills, and absence of install side effects under an empty temporary HOME.

Merge order

Merge PR #13 first, then PR #16, then this PR. Retarget this PR to main after its base is merged.

[RainLib]

验证完成：

• cargo fmt -- --check：通过
• cargo clippy --all-targets -- -D warnings：通过
• cargo test --workspace：通过
• load_skill 单元测试 5 项：通过
• load_skill CLI smoke 2 项：通过
• 从 /private/tmp 运行嵌入资源的目录与引用读取：通过
• 独立 Build & Release 工作流：Lint/Test 与 7 个发布目标全部通过

CI: https://github.com/RainLib/OfficeCli-rust/actions/runs/29794985906

唯一注解是 actions/cache@v4 的 Node.js 20 弃用警告，不影响本 PR 的构建与验证结果。