fix(seer): name the install that owns the repo on handoff 403s (#122758)

when a coding agent handoff fails with a github app permissions error,
launch_coding_agents resolved the installation by taking the first
entry from the org's github integrations

an org can have the app installed on many github accounts — one
Integration row per account — so that first entry is frequently not
the install that failed

the repo is already in scope and carries integration_id, populated
from repo.integration_id, so we can resolve the install that actually
owns it and derive the installation id and permissions URL from that

Fixes CW-1934.