feat(agents): add dc-import-postmortem-doc skill for import failure analysis

[rohitkumarbhagat]

Summary

Adds the dc-import-postmortem-doc skill to enable agents and engineers to systematically generate standardized troubleshooting post-mortem documentation following import failure investigations.

Key Changes

• New Skill (agents/skills/dc-import-postmortem-doc/SKILL.md):
  • Defines a standardized template and failure taxonomy (dependency_drift, oom_memory_pressure, upstream_source_error, etc.) to facilitate pattern extraction.
  • Enforces machine-readable YAML frontmatter (with resolution_status, infrastructure IDs, timestamps, and image versions).
  • Mandates repository-relative paths to ensure portability across developer environments.
  • Accommodates both resolved and in-progress/unresolved debugging sessions.
• Skill Registration (.agents/skills.json): Registered the new skill in the workspace skills registry.
• Git Ignore (.gitignore): Added agents/troubleshooting/ to .gitignore so generated offline post-mortem reports are not accidentally committed to the repository.

Verification

• Ran ./run_tests.sh -l to verify Python and YAML/markdown formatting passes with zero errors.

[gemini-code-assist]

Code Review

This pull request introduces a new agent skill, dc-import-postmortem-doc, designed to generate standardized troubleshooting post-mortem documents for Data Commons import failures, and updates .gitignore to ignore the generated reports. The review feedback suggests two key improvements: removing double quotes around nullable placeholders in the YAML frontmatter template to ensure they are parsed as true null values rather than literal strings, and adding a dedicated category for permission and authentication errors to the failure taxonomy.