GitLab ListBotThreads/ListBotNotes duplicate the capped pagination loop #163

Severity: Low (maintainability). Review finding D15; deferred by #157. Re-verified at 1c4e71e.

ListBotThreads (internal/forge/gitlab/gitlab.go:517) and ListBotNotes (:598) are pagination twins. Both have the same capped loop (maxListPages = 100, :274), the same fail-closed cap error, the same author filter, and the same warn-on-corrupt-marker shape. A fix to one (such as cap handling or marker parsing) must be repeated by hand in the other.

Fix: extract a generic listPaged[T] helper on next touch, behind the existing httptest coverage for both functions.