Add gapp ci list to show CI-enabled solutions

[krisrowe]

Problem

There's no way to discover which solutions have CI/CD workflows configured. gapp ci status shows the CI repo configuration but doesn't list which solutions can be triggered. To find out, you'd have to either:

• Run gapp ci trigger <name> for each known solution and see if it works
• Manually browse the CI repo for workflow files

Proposed Solution

Add a gapp ci list command that shows all solutions with active CI workflows.

Example output:

CI repo: owner/ci-repo

Solutions with CI workflows:
  solution-a    last deployed: 2026-03-14 (success)
  solution-b    last deployed: 2026-03-10 (success)
  solution-c    never deployed

Implementation Notes

• Could list workflow files in the CI repo matching the deploy-*.yml pattern
• Optionally show last run status per workflow via GitHub Actions API
• Fits naturally alongside existing gapp ci status, gapp ci trigger, gapp ci watch