fix(tools): raise tool search default results

[nightt5879]

Summary

• Raise the deferred tool-search default result limit from 5 to 20 for both regex and BM25 tool discovery.
• Add an optional max_results parameter to both tool-search schemas with default 20 and cap 100.
• Cover the default, explicit limit, cap, and schema contract with focused engine tests.

Testing

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --all-features
• cargo test -p codewhale-tui --bin codewhale-tui --all-features tool_search_
• GitHub Actions CI
  • Version drift
  • Lint
  • Test (ubuntu-latest)
  • Test (macos-latest)
  • Test (windows-latest)
  • npm wrapper smoke (ubuntu-latest)
  • GitGuardian Security Checks
  • Greptile Review

Checklist

• Updated docs or comments as needed
• Added or updated tests where relevant
• Verified TUI behavior manually if UI changes (not a UI change)

Closes #2339

[gemini-code-assist]

Code Review

This pull request introduces a configurable max_results parameter to the tool search functionalities (both regex and BM25-like search), replacing the previous hardcoded limit of 5. The tool schemas are updated to expose this parameter with a default of 20 and a maximum limit of 100, and comprehensive unit tests are added to verify this behavior. There are no review comments, so I have no feedback to provide.

[nightt5879]

Ready for review now. All GitHub Actions checks are green, including macOS and Windows test jobs. I also checked the AI reviews: Gemini reported no review comments, Greptile passed, and there are no unresolved review threads.