Add a suggest map to defineForge, capability by omission alongside produces;
GitHub implements branches via one installation read. The worker refreshes the
cache on push and install (fresh on fast-moving repos, not TTL-only) into a new
repo_suggestions table; the web reads it through a member-gated server function,
so the app never calls the forge. The builder's list-verb combobox renders the
suggestions for enum-ish signals, free text still allowed.
