fix: add ToolErrorMiddleware (backport #76)

[mergify]

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This is an automatic backport of pull request #76 done by [Mergify](https://mergify.com).

[greptile-apps]

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.
• The dependency floor matches the new middleware import.
• Tests cover expected errors, sanitization, middleware conversion, and the outer job fallback.

_{Reviews (1): Last reviewed commit: "fix: add ToolErrorMiddleware (#76)" | Re-trigger Greptile}