Gate eval runs to avoid burning tokens on unrelated PRs

[coderabbitai]

Problem

The run-evals job in the CI workflow currently executes on every PR, including those with unrelated changes (e.g., docs-only). This wastes OpenAI/Phoenix API tokens, increases CI time, and risks throttling.

Suggested Solution

Add a paths filter (e.g., dorny/paths-filter) to conditionally run the eval steps only when relevant files change (eval configs, connector configs, or eval-related code).

Context

This issue was identified during the review of PR #116.

References:

• PR: chore(evals): restructure YAML to use input/expected top-level keys #116
• Comment: chore(evals): restructure YAML to use input/expected top-level keys #116 (comment)
• Requested by: @aaronsteers