* refactor(tools): replace manual Display impl with thiserror derive
Replace the hand-rolled Display implementation for ToolError with
thiserror derive macros. The thiserror crate is already a workspace
dependency. Error messages remain identical (verified by existing
test tool_error_display_matches_legacy_text).
This reduces boilerplate and ensures consistency with other error
types in the codebase (secrets, state crates already use thiserror).
* chore: add thiserror to Cargo.lock
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Co-authored-by: Hu Qiantao <huqiantao@HudeMacBook-Air.local>
HUQIANTAO
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