ci-poller body trailing newlines

Trap: decoding GitHub issue bodies into Bash variables or updated_body=$(...) looks lossless, but command substitution strips every trailing newline and jq -r adds one on output. Fix: write .body with jq -jr to a temporary file, pass PUBLISH_ISSUE_BODY_FILE to the resolver, write rewritten .issueBody with jq -jr, and call gh issue edit --body-file. This preserves every byte except the indexed canonical SHA replacement.