fix: silently skip repos without digger config for org-wide installation

[joshuamkite-nfb]

What does this PR do?

Fixes the issue where Digger posts error comments to PRs in repositories without digger.yml configuration files when the GitHub App is installed org-wide.

Changes:

• Added silent skip logic in handlePullRequestEvent (lines 141-149) to detect missing config file errors
• When digger.yml or digger.yaml is not found, Digger now logs the skip and returns early
• Error comment posting (line 156) is still reached for OTHER error types (invalid YAML, network errors, etc.)
• This enables org-wide GitHub App installation without impacting repos that don't use Digger

Behaviour:

• Repos WITH digger.yml - continue to work normally
• Repos WITHOUT digger.yml - silently skipped (no error comments posted)
• Repos with INVALID digger.yml - still get error comments (as expected)
• Logs show: "No Digger config found, skipping repo" for tracking

Industry Standard Pattern:

This config-file-based activation pattern is used by many popular GitHub Apps when installed org-wide:

• Renovate - Only activates in repos with renovate.json or .github/renovate.json
• Dependabot - Only activates in repos with .github/dependabot.yml
• GitHub Actions - Only runs in repos with .github/workflows/*.yml files
• Pre-commit.ci - Only activates in repos with .pre-commit-config.yaml

All of these tools silently skip repos without their config files rather than posting error messages, which is the expected behavior for org-wide installations.

Testing

Unit Tests:

• All existing backend controller tests pass (5/5)
• Full backend test suite passes (18 tests)

🧠 Ai UsageDetails (if applicable):

This PR was written primarily by Claude (Roo Code mode). The solution was:

• Analyzed by AI to understand the codebase and identify the root cause
• Code changes generated by AI following existing patterns in the codebase
• Testing strategy and verification performed by AI
• All code reviewed and verified by human contributor

The human contributor understands the changes and can answer questions about:

• Error handling flow in handlePullRequestEvent
• String matching logic for config file errors
• Impact on org-wide vs per-repo installations
• Testing approach and verification strategy

Checklist

• Branched from develop
• Code follows existing patterns
• All existing tests pass
• Commit message follows conventions
• AI assistance disclosed
• Changes are minimal and focused
• No breaking changes

Related

Addresses the requirement for org-wide GitHub App installation without impacting existing repos, as discussed in the task description.