Nightly scanner should be less nit-picky about docs

[derekmisler]

Summary

The nightly codebase scanner's documentation agent was filing issues about missing doc comments in Go source files (e.g., #1912). This PR scopes the documentation agent to only analyze .md files, raises the bar so it only reports high-impact issues, and fixes a pipefail crash in the auto-issue-triage workflow.

Changes

Nightly scanner documentation agent (nightly-scanner.yaml):

• Restricted scope to .md files only — source code doc comments are no longer in scope
• Replaced the "what to look for" list with high-impact-only criteria: factually incorrect info, missing setup/build steps, broken critical links
• Expanded the "what to ignore" list to explicitly exclude style nits, typos, nice-to-have sections, and internal feature docs
• Added a default-to-NO_ISSUES directive so findings only get reported if they would genuinely block or mislead a contributor

Auto-issue-triage workflow (auto-issue-triage.yml):

• Fixed grep exit code 1 causing the "Parse agent result" step to fail under bash pipefail when the agent output contains no RESULT: marker (e.g., this run)

Test plan

• Trigger a dry-run of the nightly scan (workflow_dispatch with dry-run=true) and verify the documentation agent only analyzes .md files
• Verify the auto-issue-triage workflow no longer fails at the "Parse agent result" step when the agent doesn't output a result marker

[docker-agent]

Review Summary

Assessment: 🟢 APPROVE

This PR successfully scopes the nightly scanner's documentation agent to only analyze markdown files and fixes a pipefail crash in the auto-issue-triage workflow.

Changes reviewed:

• ✅ Documentation agent now explicitly scoped to .md files only with clear instructions to ignore source code
• ✅ High-impact-only criteria properly defined (factually incorrect info, missing setup steps, broken critical links)
• ✅ grep command correctly fixed with || true to prevent pipefail crashes when no RESULT marker is found

All changes are correct. The grep fix properly handles the case where the pattern is not found by setting an empty string, which falls through to the else block that sets action=none. No bugs detected in the changed code.

Findings

No issues found. The code changes work as intended.

[krissetto]

shouldn't we maybe expand it to the actual gh pages style docs as well?

[derekmisler]

Those were just turned into markdown files, so I think this'll work? I'll keep an eye on it.