codagent:fix-pr

Fix CI failures and review comments on the current branch's PR by dispatching a fixer subagent with all failure context, verifying the fix with the validator, and pushing.

Steps

1. Gather CI failure context

   # Get PR details
   gh pr view --json number,url,headRefName,baseRefName
   
   # Get all CI check results
   gh pr checks --json name,state,bucket,link