P2: PR polling hygiene: GitHub Enterprise remotes rejected, settled threads keep polling, Windows long paths #1523

Three small PR/git platform gaps:

1. GitHub Enterprise and ssh host aliases are rejected. isGitHubRemote (electron/worktrees-pr.js:45-51) accepts only github.com, so PR status, create and merge refuse GHE hosts and Host aliases from ~/.ssh/config (:534, :1115, :1563). Fix: resolve the host via gh auth status --hostname or GH_HOST, and accept any host gh is logged into. (M)
2. Settled threads keep polling. The PR refresher (worktrees-pr.js:1205-1214) skips archived threads and terminal PR states, but not settledOverride === "settled" (services-thread-state.js:75). Merged-worktree reclaim rides this poll, so poll settled threads at a slow cadence (e.g. every 10 min) rather than skipping them entirely. (S)
3. Windows long paths. Git calls never set core.longpaths; doctor.js:98-117 only warns. Inject GIT_CONFIG_COUNT/KEY/VALUE for core.longpaths=true in the git env on win32. (S)

Related: #1431.