fix(find): reject unsafe bare native actions

[antonio-orionus]

Summary

• fall back to native find for compound expressions/actions that RTK should not emulate
• reject bare native actions like -delete/-exec unless a narrowing predicate is present
• clarify rtk find and rtk test behavior in user docs

Why

Bare native action forms such as rtk find -delete can default to the current directory when delegated to native find, creating a destructive footgun.

Verification

• rtk cargo fmt --all --check
• rtk cargo test find_cmd -- --nocapture
• rtk cargo clippy --all-targets
• rtk cargo test --all
• rtk git diff --check

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