Simplify dc-import-diagnostics references and expand troubleshooting

[rohitkumarbhagat]

Summary

• Move import-specific operational guidance into flat, service-level references within dc-import-diagnostics.
• Clarify run and version terminology and routing for common diagnostic requests.
• Add baseline troubleshooting triage, Batch runtime hypotheses, validation-failure guidance, and golden evaluation queries.
• Add bounded OOM and Java GC-thrashing investigation using Cloud Batch evidence.
• Validate reachable Markdown files and section fragments from registered skill entry points.

Testing

• python -m unittest discover -s agents/common/scripts -p '*_test.py'
• ./run_tests.sh -l
• git diff --check

[gemini-code-assist]

Code Review

This pull request reorganizes and consolidates the repository's agent 'recipes' into 'operational references' under the dc-import-diagnostics skill. Individual markdown files for GCS, Batch, Scheduler, and Spanner operations are grouped into consolidated reference files, and terminology is updated from 'recipes' to 'operational references' throughout the codebase. Tests are updated to verify these new references and enforce markdown link and heading contracts. Additionally, a new golden queries evaluation file and a validation troubleshooting guide are introduced. There are no review comments provided, so I have no feedback to provide on the review itself.